There are 6 color proms on Punchout.
3 for the upper monitor, and 3 for the lower monitor.
All are 82s131 ( 512 x 4 )
Each prom controls one primary color for the monitor ( Red, Blue, Green ).
I believe the proms work as follows
Upper Monitor : 6E (Red), 6F(Green), 7F(Blue)
Lower Monitor : 7E (Red), 8E(Green), 8F(Blue)
These seem to go bad fairly often as I get quite a few requests for these.
Cheers,
Steph
www.Hobbyroms.com