I assume you mean a 'soap-bush' ( https://uvalde.tamu.edu/herbarium/guan.htm is it, right??)?
If so, it should be outside so it gets its 'rest' (dormancy'. All perennials (deciduous, per se) need to feel the winter to maintain its genetic program(s) to keep it vigorous. If temps rarely, if ever, get below freezing, then just leave it outside (!!!!) and let it get cold - it needs such temps
It is normal for newer growth to be a bit brighter-green which slowly darkens to a deeper green...no worries there.
Do not keep watering by placing in water...it will lead to bad things later on probably. Water like regular pots - from 'overhead', like pouring it into the pot. It helps pull 'fresh air' into the soil which is good for the roots and microbial things in the soil. A small difference, I know, but it does matter
Only water when soil is pretty much dry all the way through. (its a drought-tolerant species, of course)
Good luck with the Guayacan! I am kind of preferential to sagebrush-like plants or anything xeriscapic such as it. They are prepared to deal with drought or other things that would kill off less-hardy plants.