Adds colorblindness as a mild brain trauma (#76527)

## About The Pull Request

What the title says. 
The brain trauma makes the whole screen monochrome until cured.

![image](https://github.com/tgstation/tgstation/assets/82850673/442d24a8-6625-454c-bc28-64b786b03f49)

## Why It's Good For The Game

I feel like the current pool for mild brain traumas is quite lame, this
helps spice it up a bit with something that is quite annoying and
distracting but not game breaking (as mild brain traumas should
generally be).

## Changelog

🆑
add: Added colorblindness as a mild brain trauma.
/🆑

---------

Co-authored-by: san7890 <the@san7890.com>

code/modules/client/client_colour.dm

@@ -198,6 +198,9 @@
 	fade_in = 20
 	fade_out = 20
 
+/datum/client_colour/monochrome/colorblind
+	priority = PRIORITY_HIGH
+
 /datum/client_colour/monochrome/trance
 	priority = PRIORITY_NORMAL