[Sunred]

To start off and also give an example, here are a few:

<Liveman>
[Color change]
Green Sai > Blue Sai
Blue Dolphin > Pink Dolphin
As much as I like and think it was clever for Liveman to go with the five rings of the Olympics considering that the year they were airing was 1988, I sometimes think if they started with all five members from the get-go, they could have pulled off the Goggle V palette. Green Sai looks like it would go well with blue and last time I checked pink dolphins do exist.

<Megaranger>
[Color change]
Megablack > Megagreen
Given that the show was about "digital" "video games" "cheerful high school drama" I think green could have worked well.

<Gingaman>
[Color change]
Gingagreen > Gingablue
Gingablue > Gingablack
Gingapink > Gingawhite
I think they could have utilized the Kakuranger palette, and considering Ogawa who was Sasuke/Ninjared is in it, it would have been fun to see that.

<Dekaranger>
[Color change]
Dekamaster(light metallic blue) > Dekamaster(jet black)
I think jet black with gold and red trims instead of light metallic blue with white and red would have made that 100% cool factor of the boss up to 150%.