Their confrontation between blonde and brunette is canonical in American cinema, and is very well explained by the "Betty and Veronica" trope, which originated in Archie Comics and is transformed in modern "Riverdale". The gist of the trope is that in a love triangle, there's always the more demure "Betty" and the sophisticated liberated "Veronica". But like "Riverdale" in 2020, Elle and Vivian were able to get past the stereotypes, see each other, stop fighting over a character unworthy of them, and graduate from Harvard as best girlfriends.
True, in "Legally Blonde," beautiful actress Selma Blair plays the supposedly ugly girl - but that's a relic of films from the early 2000s. And the name Vivian is a tribute to
"Pretty Woman" - another film where a woman breaks all stereotypes.