Dear, it is been more than 3 months trying to level up yellow heroes using same color/ different color feeders but can’t increase their special power unless when ascended to the next level.
Is it a bug or can you help. The other colors were probably leveled up.
Thank you
just up leonidas yesterday three times, with rainbow 1* heroes, just think you’re not lucky man 
Try using 1x 1* yellow for awhile. I’m doing that with purple on my Domitia who is reluctant to level. Every so often I’ll feed her a rainbow 10x 1*, just to see if anything shakes loose.
it’s totally random, level up sp ability especially with 5* is more easy than you ca do with 3*.
it’s a loooong way to up them until 4 *80…so no risk at feed them with many rainbow1…
more boring for 3*. try to up only with same color heroes.
my opinion
