JavaFX dialog for numeric typed data input

Question

I have this small subclass of JavaFX's javafx.scene.control.Dialog that requires the enum specifying the data type of the input data:

package com.github.coderodde.jfx.ui;

import java.util.Objects;
import java.util.Optional;
import javafx.event.EventHandler;
import javafx.scene.control.ButtonBar.ButtonData;
import javafx.scene.control.ButtonType;
import javafx.scene.control.Dialog;
import javafx.scene.control.Label;
import javafx.scene.control.TextField;
import javafx.scene.input.KeyEvent;
import javafx.scene.layout.GridPane;
import javafx.scene.paint.Color;

public final class TypedInputDialog extends Dialog<Number> {

    private static final Color DEFAULT_COLOR_TEXT_NORMAL = Color.BLACK;
    private static final Color DEFAULT_COLOR_TEXT_ERROR  = Color.RED;
    
    public enum InputType {
        INTEGER,
        LONG,
        FLOAT,
        DOUBLE;
    }
    
    private String promptText = "";
    private final InputType inputType;
    private final Label errorMessageLabel = new Label();
    private final TextField inputTextField = new TextField();
    private EventHandler<KeyEvent> keyEventHandler;
    private Color colorTextNormal       = DEFAULT_COLOR_TEXT_NORMAL;
    private Color colorTextError        = DEFAULT_COLOR_TEXT_ERROR;
    private Optional<Number> data = Optional.empty();
    
    public TypedInputDialog(InputType inputType) {
        
        this.inputType = inputType;
        buildKeyEventHandler(); 
        inputTextField.setPromptText(promptText);
        inputTextField.setOnKeyTyped(keyEventHandler);
        
        GridPane gridPane = new GridPane();
        gridPane.add(errorMessageLabel, 0, 0);
        gridPane.add(inputTextField, 0, 1);
        getDialogPane().setContent(gridPane);
        
        ButtonType buttonTypeOK = new ButtonType("OK", ButtonData.OK_DONE);
        this.getDialogPane().getButtonTypes().add(buttonTypeOK);
        
        this.setResultConverter((ButtonType p) -> {
            if (p == buttonTypeOK) {
                return data.orElse(null);
            }
            
            return null;
        });
    }
    
    public String getPromptText() {
        return promptText;
    }
    
    public void setPromptText(String promptText) {
        this.promptText = 
                Objects.requireNonNull(
                        promptText, 
                        "The input prompt text is null.");
    }
    
    public Color getNormalTextColor() {
        return colorTextNormal;
    }
    
    public Color getErrorTextColor() {
        return colorTextError;
    }
    
    public void setNormalTextColor(Color normalTextColor) {
        this.colorTextNormal = 
                Objects.requireNonNull(
                        normalTextColor, 
                        "The input color is null.");
    }
    
    public void setErrorTextColor(Color errorTextColor) {
        this.colorTextError = 
                Objects.requireNonNull(
                        errorTextColor, 
                        "The input color is null.");
    }
    
    private void buildKeyEventHandler() {
        this.keyEventHandler = (keyEvent) -> {
            switch (inputType) {
                case DOUBLE:
                    processDouble();
                    break;
                    
                case FLOAT:
                    processFloat();
                    break;
                    
                case INTEGER:
                    processInteger();
                    break;
                    
                case LONG:
                    processLong();
                    break;
                    
                default:
                    throw new IllegalStateException(
                            "Unknown type: " + inputType);
            }
        };
    }
    
    private void processInteger() {
        if (inputTextField.getText().isBlank()) {
            data = Optional.empty();
            writeNormalMessage("");
            return;
        }
        
        int value;
        
        try {
            value = Integer.parseInt(inputTextField.getText());
            writeNormalMessage("");
            data = Optional.ofNullable(value);
        } catch (NumberFormatException ex) {
            writeErrorMessage(
                    "Wrong 32-bit integer value: " + inputTextField.getText());
        }
    }
    
    private void processLong() {
        if (inputTextField.getText().isBlank()) {
            data = Optional.empty();
            writeNormalMessage("");
            return;
        }
        
        long value;
        
        try {
            value = Long.parseLong(inputTextField.getText());
            writeNormalMessage("");
            data = Optional.ofNullable(value);
        } catch (NumberFormatException ex) {
            writeErrorMessage(
                    "Wrong 64-bit integer value: " + inputTextField.getText());
        }
    }
    
    private void processFloat() {
        if (inputTextField.getText().isBlank()) {
            data = Optional.empty();
            writeNormalMessage("");
            return;
        }
        
        float value;
        
        try {
            value = Float.parseFloat(inputTextField.getText());
            writeNormalMessage("");
            data = Optional.ofNullable(value);
        } catch (NumberFormatException ex) {
            writeErrorMessage(
                    "Wrong 32-bit floating-point value: " 
                            + inputTextField.getText());
        }
    }
    
    private void processDouble() {
        if (inputTextField.getText().isBlank()) {
            data = Optional.empty();
            writeNormalMessage("");
            return;
        }
        
        double value;
        
        try {
            value = Double.parseDouble(inputTextField.getText());
            writeNormalMessage("");
            data = Optional.ofNullable(value);
        } catch (NumberFormatException ex) {
            writeErrorMessage(
                    "Wrong 64-bit floating-point value: " 
                            + inputTextField.getText());
        }
    }
    
    private void writeNormalMessage(String statusMessage) {
        writeStatusMessage(
                statusMessage, 
                colorTextNormal);
    }
    
    private void writeErrorMessage(String statusMessage) {
        writeStatusMessage(
                statusMessage, 
                colorTextError);
    }
    
    private void writeStatusMessage(String statusMessage, Color textColor) {
        
        errorMessageLabel.setStyle(
                "-fx-text-fill: " 
                        + convertColorToRGBText(textColor)
                        + ";");
        
        errorMessageLabel.setText(statusMessage);
    }
    
    private static String convertColorToRGBText(Color color) {
        return String.format(
                "#%02X%02X%02X", 
                (int)(color.getRed() * 255),
                (int)(color.getGreen() * 255),
                (int)(color.getBlue() * 255));
    }
}

package com.github.coderodde.jfx.ui;

import java.util.Optional;
import javafx.application.Application;
import static javafx.application.Application.launch;
import javafx.stage.Stage;

public class Demo extends Application {

    public static void main(String[] args) {
        launch(args);
    }

    @Override
    public void start(Stage stage) throws Exception {
        TypedInputDialog dialog = 
        new TypedInputDialog(TypedInputDialog.InputType.DOUBLE);
        
        dialog.setPromptText("(Enter value here)");
        dialog.setTitle("Demo TypedInputDialog");
        dialog.setHeaderText("Enter a double floating-point value:");
        Optional<Number> result = dialog.showAndWait();
        
        System.out.println("Input value: " + result.orElse(null));
    }
}

Critique request

So what do you think? What shall I improve?

Thanks in advance.