How to Loop Through 5 Cells in a Row Using Excel VBA

In your code, Y appears to be an undefined variable. To check for the value, put it in double quotes:

If c.Value = "Y" Then

When you don't define c as a range, the statement

For Each c in ActiveSheet.Range("Q5:U5").Cells

while valid, will actually result in c having the value of each of the cells. To solve this problem, declare the type explicitly:

Dim c as Range

Next, when you do the comparison (as already pointed out), use

If c.Value = "Y"

Note - if you declare

Option Compare Text

right at the top of your module, the comparison will be case-insensitive; otherwise, a "Y" will not match a "y".

The whole module would look like this, then:

Option Explicit
Option Compare Text

Sub colorMe()
Dim c as Range
For Each c In Range("Q5:U5").Cells
  c.Select
  If c.Value = "Y" Then
    With Selection.Interior
      .Pattern = xlSolid
      .PatternColorIndex = xlAutomatic
      .Color = 5287936
      .TintAndShade = 0
      .PatternTintAndShade = 0
    End With
  End If
Next
End Sub

I am sure it doesn't need to be pointed out that you could achieve the same thing with conditional formatting...