Aesthetic for an LMS is tricky: you want it to stand out, but you don’t want to overload your audience either; after all, the information within is what’s most valuable.
Color coding is a classic strategy. If students use it via colored pens, highlighters, and flags to help memorize information, why shouldn’t an Learning Management System provide a corresponding system? Also, if the LMS is divided into tools, topics, etc., by colored tabs, maybe, they would be easier to find. Tabs should stand out from the page enough to make the LMS as conveniently navigable as possible.
Search buttons and section titles shouldn’t be obscured by bold graphics or, in turn, drab monochrome. If the information is a hassle to find, whatever educational merit there is will be wasted on learners who’ve given up out of frustration.