I have purple IMPACT I2s that don't have IMPACT cards. Would the video option boards(I don't recall the names, Indigo2Video for IMPACT I think?) I use need to be made for IMPACT systems even if I don't have an IMPACT card? Or can I use the earlier non-IMPACT card(Indigo2video??) on a IMPACT(purple) system w/ non-IMPACT gfx? Whew - did that make sense?
The purple systems without Impact graphics were often called "Impact ready". So you do not actually have an Impact system until you put in Impact graphics. Does that make it clearer? With non-Impact graphics you need non-Impact video. With Impact graphics, you need Impact video. That's all there is to it. Case colour doesn't come into play in determining which video options go with which graphics options.
(Aside from case colour, the Impact systems also have an upgraded power supply and slightly different layout of the riser card that things plug into. That's necessary to support the Impact graphics but still backwards compatible with the older stuff.)
Also beware that there's more than one video option for the Impact systems. There's the Indigo2 Video for Impact option and the Impact Video for Indigo2 option. They are not the same. But that's only relevant if you first upgrade to Impact graphics. There's an old but useful guide, the Lurker's Guide, at http://lurkertech.com/lg/devices.html
Sun SPARCstation 20, Blade 2500