There have been mods that change contrast and more that have been used by players. One player kept theirs updated and shared updates via these forums.
However, that does not mean they do not violate ToS and I would expect no player could give you a definitive answer. Doubt Zos would either since they do not even support the use of Addons that they ask players to create.
xMovingTarget wrote: »Been using reshade for years. Even in eso. Never any problems. Even used a different tool to remove to fog in the distance. Never a problem. Just go ahead and use reshade. It won't get you banned.
It adjusts or adds shaders. If you own a nvidia card, you can even do this with geforce experience.