First thank you very much for your answer!
So yes, the problem is that I can't select a specific color.
I link 2 images with this message:
the first one is an image i took when i go in the categories. You can see the different french categories, and in red, it is the colours which i could selected when i had the english version but as you can see, there are only two colours now and whenever i tried to select them, the colour doesn't go on my calendar.
The second image shows you what i have when I go in the "options". There, there isn't any colours at all and i would know how to put back the colours in it, so i will able to change the colours of some event on my calendar.
I hope my english is not too bad, i tried to do my best.
P-S : sorry but i can just put one image with this message, so the second image is in my second msg.