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I have several watercolor swatches that have the shape I want to use in a design. But I want to adjust the overall color of the shape to be one of our brand colors. I know that you can use the Hue/Saturation tool and drag the different aspects, but what if I want to use one of my RGB/HEX numbers as a guide? 
I'd like to change this so that the "main" color could be 6f9fcd or 96ad3e or eeba30 for example.
You can do this with a gradient map adjustment layer.
A gradient map adjustment layer will take the underlying tone (just the brightness) and map it to a gradient of your choice.
The left image is the original, the middle is a greyscale version, and the right image has a gradient map applied (a gradient from red to yellow).
Gradient maps are fairly unique adjustment layers, in that they let you use absolute colour values, which is what you’re after.
Here’s your image with a the colour changed, using a gradient map (and therefor an absolute HEX value colour).
