Whenever increasing the light, doing it gradually can help avoid burning the leaves.
'Tricolor' is a cultivar name, and 'Rainbow' may be one I've not heard. It's not listed on this site, but that's not definitive:
http://www.triadplantco.com/li...
If yours was labeled with a cultivar name, it's full name is D. marginata 'Cultivar.' Can't see it closely enough in either discussion to know which it is. There's also 'Colorama' which is very similar.
