If you have Access 2000 or later it can be done using Conditional Formatting.
Click on the control to be formatted to select it, then goto Formatting >
Conditional Formatting.
If the formatting of the ControlA is dependant on a value of ControlA, use
"Field Value Is" then enter the conditions for formatting, then set the
ForeColor/BackColor/Bold/Italic/Underline/Enabled options for that condition .
If the formatting of ControlA is dependant on a condition of, for instance,
ControlB, use "Expression Is" and then, for example, ControlB > 5, or
ControlB = "Completed" and then, once again, set the
ForeColor/BackColor/Bold/Italic/Underline/Enabled options.

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Answers/posts based on Access 2000