The species which are infamous for "going sexual" are in the genus Caulerpa. While some Caulerpas, like Caulerpa Ashmeaddii, are highly unlikely to do so, you might want to avoid Caulerpas in general. That said, there are plenty of other colorful macro algae. Dragon's Breath macro algae, ORA Blue Hypnea, Blue Ochtodes, Codium Lucassi, Gracilaria Sp., and Halymenia Sp., to name a few, are all very colorful. For info on many different types of macro algae, check out marineplantbook.com. Gulf Coast Ecosystems and LA Reefs have the broadest variety of macro algae for sale, so you should look at their stock to get an idea of what you might like, too.