Let me think hmm before I check results
If we are talking normal TC20 heroes all colours are fairly even and have their own weaknesses
Yellow - no 4* healer but best vanilla 5* healer
Purple - no 4* snipers but 5* Sartana is great, great healers
Red - Great all round utility (Khagan the weak link)
Blue - Great all round utility (Thorne a weak link)
Green - aside from Lianna, who is boss, lack of 5* green heavy hitters
If we introduce HOTM, as was mentioned above, the scales tip in Green’s favour somewhat due to Alby, Zel, Mother, Evelyn, MLF due to their insane powers.
Red is still solidly strong due to Gravy, Zim and Ares
Blue is solid too with Athena and Alasie, although Perseus and Aegir are not as useful
Yellow is solid with Del, Guin, Drake
Purple is so-so but Panther and Hel are nothing to be sneezed at.
I reckon on an overall basis Red is pretty good all around, but Green is pretty skewed for HOTM