Help me please,

I can use most functions on excel. I'm looking for a way to write a formula that will use conditional formatting to shade the cell.

Entries could be:

H
S
O
T

These entries will be used in conjunction to the above entries

R
I
S

Thus I want to shade the cell based off of the R, I or S how ever they only appear as:

HR, HI, HS or
SR, SI, SS

That being stated I have tried to use a search function for the Text R, I and S. and shade the cell accordingly.

This would be used in an Array of B2:AF7 (six month calendar)