EDIT:: FORGOT TO SAY, This SHOULD work in any type of photoshop, I don't know about Gimp though and I know nothing about SAI. :C soyeah.
I am really bad at making tutorials or explaining things to people. I'm absolutely HOPELESS to this stuff. :C
but some one asked for me to make a checker tutorial and how I did it. (and I will be making another tutorial for the rainbow lettering hehe)
I'm so sorry for my bad handwriting and any spelling or grammatical errors in this :C
hope this makes sense XD;;;;;