Advance makes a ballist that can be used for 3 or 4 tube. I want to use the 3 tube but the colors coming off the ballist are different. The old ballist has 3 blues one side, 1 red the other, and the black and white for power. The new one is different.

Not being a wire guy, but read the label on the new ballast. All have wiring diagrams for uses that they are capable of

John

Provided your new ballast has (2)red, (2) blue (2) yellow, (1) black (1) white, and has 32W T8 lamps:

You'll have to do some rewiring to get the 4/3 lamp ballast to work with a fixture originally designed with a 3 lamp ballast.

One of the lampholders on the "red" end of the original fixture will need to be disconnected.
One of your yellow leads will go to this lampholder, the other yellow will connect to the remaining 2 lampholders.
Connect 1 blue lead from the ballast to the lampholder opposite the lampholder that's wired (to the yellow) by itself. Cap the other blue lead from the ballast.
Connect the remaining 2 lampholders, each to one of the red leads from the ballast.

Watch for smoke

i will just read the label on the ballast itself because some of them dont have the same pattern for hook up

Merci , Marc