Modulate colors of players for nightvision in vampire

[rtxa]

1. Implement by changing sv_skycolor_* but only send it to vampire https://forums.alliedmods.net/showthread.php?t=343424
   To do this, we need to hook SVC_NEWMOVEVARS with ReAPI https://github.com/s1lentq/reapi/blob/1d17078fd6b20531f6b965834487eb58d85eec6a/reapi/src/member_list.h#L738

2. But if this already requires models to be set with some flag, then maybe it would be better to modify the model instead?