You want to avoid illuminating a play space red or blue, because the colours of player models will become hard to distinguish.
Give point_spotlight a try. It's not a light, it's a halo/corona/tyndall effect that simulates a spotlight but doesn't generate any actual light, so it won't affect lightmap sizes.
Give each coloured set a name (e.g. light_red and light_blue), then you can send outputs to them from the control point entity when it changes owner.
FYI point_spotlight has a maximum width of 72 or something like that so if the effect isn't wide enough, then try reducing its length.