I know that there is a limit to 3 conditions, however I was wondering of
there was a way to write a formula for the following:

I have a schedule for classes grades 1,3,&5. Each grade has 4 classes,
A,B,C,D, so a total of 12 classes.

I made a schedule in Excel and I want to color code all the grades
differently, e.g., grade 1 in yellow, 2 in blue, and 5 in green.

In the cells for different periods and different days of the week I've typed
1A, 1B, 1C, 1D, 3A, 3B, etc.

Now when I open Conditional formatting, if I want to use cell is equal to, I
could only format the first three, 1A, 1B, 1C...

Could I write a formula that does the formatting: all cells with the number
1 and a letter are yellow, all cells with the number 3 plus a letter are
blue?

Thanks!