Couldn't quite understand what was intended by "merge" - but seeing what
@IamSam did, really just was a monotone.
Haven't played with mono- or duotones much so checked into the process:
- Open your image
- Go to Image>Mode>Grayscale and click "Yes" to discard the color information.
Then go to Image > Mode > Duotone and choose "monotone".
Click on the color patch and when the color dialog box shows up, just choose the color you want or enter the values, or enter the hex code
I think this is what you're trying to accomplish based on the discussion. In any case, Photoshop always seems to give you more than one way to do something...
- Jeff