Add pattern to object without seeing underlying color

[sarao3511410]

Hello! I am trying to change the pattern on object in a flattened image. I have figured out how to add the pattern, but I am needing help on how to make it to where I cant see the original pattern on the object. It is making the color of the new pattern different. I need to keep shadows of original object.

My new pattern is grey. Original pattern was light blue. Thanks!

[Bojan Živković]

If you want to desaturate blue color why not use Hue/Saturation and to drag Saturation slider to the left?