First thing I do once I’ve cropped, made my gif and sharpened it is to adjust the curves. 

I always set the white point and the black point using the eyedropper tool. This adjusts both the brightness but also the RGB layers (red, green and blue) and begins colour-correcting the gif. 

I then do another curves layer and I use the auto-correct curves button. This automatically adjusts the curves and brightens the entire gif. 

Once I’ve done my curves I move on to the levels. I increase the black point (the first little arrow as you look at it) and the grey point (the middle arrow). The black point deepens the darker areas of the gif. The grey point can either brighten the grey areas or darken them - I tend to brighten them.

Then I adjust the brightness and contrast to make the whole thing brighter and deepen the colours. 

The channel mixer is a new discovery I made (I didn’t make it, I just found a tutorial that did). It helps to colour-correct the gif and make it less orange/blue etc. If you’ve seen Shadow and Bone (namely season one) you know how green and orange some of it is. This layer helps to combat that and make it a more natural colour. 

For this gif, because it was all a bit yellow/orange, I decreased the reds and greens and increased the blues. I only go up or down by one or two - if you go too much in one direction or the other it’ll begin to change the colour of the entire gif rather than subtly correct it.

To colour-correct a bit more I use the colour balance layer. Again, I decrease the red and increase the blue. I tend to stick to going up in fives on this layer. +/- five tends to do what I need it to regarding colouring. 

And finally I adjust the vibrance by five or ten just to make the entire gif pop that bit more.

Here's the gif before and after!

It's made a huge difference and made the entire gif seem a lot brighter and less yellow.

And just to prove it works no matter what - the left side has been coloured the right hasn't. The difference is noticeable, especially on Yennefer.

Tada, colouring tutorial! Whilst the numbers vary from gif to gif the order and layers used remain the same. 

Here are some useful links to other tutorials. These are like my bible and I swear by them! 

Gifmaking for beginners by @hayaosmiyazaki (the holy grail of tutorials for me)

Gif Making Guide for Beginners by @saw-x

And this tutorial by @aubrey-plaza goes into more detail about the channel mixer and how it actually works!