The engine has sRGB conversion functions, they are not exposed to blueprints. You can write some simple blueprint library functions to expose them. Slate doesn’t render the final color in linear space - the final color we render is in Gamma space.
If you want to simply go between Gamma and Linear colors easier, you can use FColor, which may or may not be exposed to blueprints, but that’s the classic RGBA8 gamma space color structure in the engine.