1) You did not include the last important bit of code where you select
the range  to be evaluated by Color_Cell.

So I am going to assume that your defined Range consists of more than
one cell, and it is defined as follows:
Dim Cell
Cell = Selection.Address

Since you have multiple cell  selected in your range, when you try and
evaluate Color_Cell, you can only evaluate the first cell in the range.
It would be better to loop through all cells  in the range Cell, and
evaluate each one on its own.

2) error  13 is a Type Mismatch error. For more information, search for
"trappable errors" in the VBE. That will explain it very well, and will
provide some insight on how to avoid it.