Hi there!

Can please someone tell me how to achieve this dark tones? Blue skin tone, green, red, etc.

https://ibb.co/izQ93K

Thanks a lot!

looks to me that they made a new layer and set the blend mode to color and then painted in the color they wanted.  Pretty heavy handed editing with no attention to shading or color variation.  Hard line color changes instead of shifting tones as things curve in and out of the light is a give away.

Its a mix between color lookups and the paint filter in photoshop. Not my cup of tea, but if you go to deviantart, and search in the psd resources for color, theres tons of PSD files that help you achieve that look.

It's using the tones and even some curve adjustment for each of the colors such as red, blue and green, changing only the color that you want to change (increase/decrease).  So don't use RGB go with custom changes.  Also, you can add a color layer and apply with a mask to allow only the tone of the color to come through blocking all other areas.

Color lookup , channels + curves .