With the OkColor plugin you will be able to convert linear RGB colors to the OKLCH color space. Why the OKLCH Space? OKLCH is a perceptually consistent, larger color space. which keeps the brightness of the color the same, regardless of hue. With this you can perform interpolation more consistently and avoid some colors sticking out because of their brightness.
This plugin has Blueprint integration to allow conversion of colors on the CPU and direct material intergration with a set of nodes providing conversion to and from OKLCH on the GPU.
You can either pick your color using the standard RGB Color picker in UE and get it automatically converted to OKLCH using the inbuilt types, or set the LCH components directly,
You can get more information and ressources from the documentation: OKColor | OKColor Docs
And the plugin is a available on Fab: OKColors | Fab