I have a string of characters in Column D which will look like so:

==MTWRF
==MTWR=
Y=MT=RF
==MTW=F
Y=MT=RF

The = represents a day off.
Columns F thru L are labelled With days of the week (starting w/ Sat)

F=Sat
G=Sun
H=Mon
I=Tues
J=Wed
K=Thurs
L=Fri

I would like to shade the corresponding cell black where the = sign represents a day.

==MTWRF would shade F (Sat) and G (Sun)
==MTWR= would shade F (Sat), G (Sun) and L (Fri)

It seems I should be able to use conditional formatting, but I am not certain what formula to use.

Thanks for any help you can provide (I can attach the spreadsheet if that would make it simpler)