That is not the ordinary process for board houses. There is no standard way to specify that, and many board houses may not even want to bother, or charge you a lot extra.

Sounds expensive for two colors silkscreen on the same PCB, but certainly doable if you can find someone willing to do it. It would be cheaper to use one color for silkscreen, and then get creative in the soldermask layer.

I have not seen or used, but I think it could be done on technical reson. But it would not fit with some production processes where boards from different customers are panelized. Often the silk screen colors offered are very limited, mostly are black or white so they may not be set up for what you want.