So I installed
this plugin.
Now my question is: Where can I change the colour of the spoiler and the code tags and the quote text?
I already tried changing it in global.css but didn't found anything.
Go to: ACP > Themes > Edit Your Theme > global.css > and find ;
For quote template name is blockquote.
For spolier as you can see you have to add for spoiler to your global.css .spoiler_header and .spoiler_body so change some variables of that what you added to change to color which you want.
For code template name is codeblock.
I tried changing codeblock but it remains white.
Can you post your codeblock template here? And also i forgot to mention codeblock have 3 template codeblock, .codeblock .title and .codeblock code so take a look on them to see is there anything to change to make it good for you.