Material Hue Shift by value

I’m looking to create a material that will apply color based on a grayscale texture map.

I’ve found that a Lerp node with the grayscale as the alpha does somewhat what I want but I need finer control.

Ideally using only a linear color to pull the color information from.

I explain a simplified version here, and another member has a more complex one showcased:

Hey this is great! Thanks.

be sure to set the answer as correct if it was helpful.