luminance manipulation?

[Mark G Orr]

Hello, I checked the archives for an answer to my problem, but that did
not work.  I want to change the luminance of one letter within a 4 letter
word relative to the other three letters in the word.  Furthermore, i want
the degree to which the letter is different from the other words
modifiable with respect to each individual subjects performance.  Any help
will be greatly apprectiated.

-Mark Orr