Where is your checkbox? On UserForm or Worksheet?

Anyway, to color a cell, for example, yellow:

range("A1").Interior.ColorIndex = 6

To remove the color:
range("A1").Interior.ColorIndex = xlNone

To discover more "colorindex", you may try using the "Record Macro" function of Excel.

In fact, the Record Macro function is a very very good way to learn VBA.

Regards,
Edwin Tam