Merging gradient map with image layer below it changes colours

[Sam5DF0]

https://imgur.com/cumz4NY
https://imgur.com/Cqcosu7

First link is the colours I want it to be before merging layers

Second link is the unsaturated colours after merging.

What is the cause of this significant change from merging a gradient map layer and an image layer?

[c.pfaffenbichler]

Could you please post screenshots taken at View > 100% with the pertinent Panels (Layers, Channels, Options Bar, …) visible of before and after merging on this Forum? 

[Sam5DF0]

https://imgur.com/wWfeOpA 

https://imgur.com/WjcMikD 

Interesting....it seems to be unaffected at 100% so maybe it is just a rendering difference of how Photoshop deals with flattened/unflattened layered pixels. I hadn't done any prints yet so I cant comment on whether there is a difference between the two settings in reality, but it seems like there mightn't be an issue at all now..

[Sam5DF0]

this seems to make sense as now I look at the file more, the colour changes the most in the areas with the highest detail eg. rocks and tree textures, but basically doesnt change on the simple textures like the sky and clouds

[c.pfaffenbichler · Accepted solution]

For speed’s sake Photoshop can use downsampled stand-ins for Layer calculations at sizes lower than View > 100%. 

And as you already noticed the effect is strongest for noisy elements.