Adds a unit test for client colours. (#77484)

## About The Pull Request
I'm adding a unit test for the sanity of client colours, ancient datums
which I had refactored a long time ago. This also affects the
`color_to_full_rgba_matrix()` proc, which I had also worked on.

## Why It's Good For The Game
Ever since that aforementioned years old refactor, there have always
been a few issues with client colours.
The most annoying one being the monochromacy client color lingering even
after the blindness status effect is ok.
It's unlikely this will fix that. However, this should clear a few other
runtimes with the feature.

## Changelog
N/A.

code/modules/client/client_colour.dm

@@ -16,8 +16,8 @@
  * Define subtypes of this datum
  */
 /datum/client_colour
-	///Any client.color-valid value
-	var/colour = ""
+	///The color we want to give to the client. This has to be either a hexadecimal color or a color matrix.
+	var/colour
 	///The mob that owns this client_colour.
 	var/mob/owner
 	/**
@@ -32,8 +32,8 @@
 	///Same as above, but on removal.
 	var/fade_out = 0
 
-/datum/client_colour/New(mob/_owner)
-	owner = _owner
+/datum/client_colour/New(mob/owner)
+	src.owner = owner
 
 /datum/client_colour/Destroy()
 	if(!QDELETED(owner))
@@ -150,7 +150,6 @@
 
 /datum/client_colour/glass_colour
 	priority = PRIORITY_LOW
-	colour = "red"
 
 /datum/client_colour/glass_colour/green
 	colour = "#aaffaa"
@@ -212,9 +211,10 @@
 	colour = list(0,0,0,0,0,0,0,0,0,1,0,0) //pure red.
 	fade_out = 10
 
-/datum/client_colour/bloodlust/New(mob/_owner)
+/datum/client_colour/bloodlust/New(mob/owner)
 	..()
-	addtimer(CALLBACK(src, PROC_REF(update_colour), list(1,0,0,0.8,0.2,0, 0.8,0,0.2,0.1,0,0), 10, SINE_EASING|EASE_OUT), 1)
+	if(owner)
+		addtimer(CALLBACK(src, PROC_REF(update_colour), list(1,0,0,0.8,0.2,0, 0.8,0,0.2,0.1,0,0), 10, SINE_EASING|EASE_OUT), 1)
 
 /datum/client_colour/rave
 	priority = PRIORITY_LOW