Cocerello making textures for Quake is not technically difficult at all, you just have to have an eye for it.
Doing a hue or saturation change to an existing set (ie. the IK set) is not hard, but whether or not it looks good is a different question.
All you need to make or modify textures is TexMex and a good photo editor that can work with palettes. You must download the Quake palette (just search it its hosted everywhere...) And I suggest you also create a palette file minus the last 32 fullbright colours.
Use Texmex to obtain textures from a map, or import your new textures into a wad. Starting with other textures is good for beginners.
You will need to load the texture into a photo editor, convert it to RGB based image before making hue and saturation changes. Then reapply the indexed palette when finished. Applying the Quake palette can have devastating effects on your image and you need to be prepared to hand paint pixels that don't look good. Never just drop an image into Texmex, this is a poor approach that leads to ugly textures.
Quake doesn't have any actual red in the palette, just crimsons and browns. One of the true reds is a fullbright, and Texmex sometimes confuses your red with this color, so you need to be careful when importing into Texmex.
I spend a lot of time with some textures especially working with red. When I make a texture and hand paint from scratch it can take weeks. These 'red' banners took me three weeks to get right and they are mostly violet and pink. Some of the other textures you see here are hue/saturation changes I made in only a few minutes:
https://i.imgur.com/Z73qEOP.png
I use mtPaint which is free software to create pixel art.
Take your time and have fun.