Migrate GUI colors test to original CSS color format

[GuillaumeGomez]

Follow-up of #111459.

r? @notriddle

[notriddle]

@bors r+

[bors]

📌 Commit 680b3ac has been approved by notriddle

It is now in the queue for this repository.

[bors]

🌲 The tree is currently closed for pull requests below priority 100. This pull request will be tested once the tree is reopened.

[bors]

⌛ Testing commit 680b3ac with merge b588641...

[bors]

☀️ Test successful - checks-actions
Approved by: notriddle
Pushing b588641 to master...

[rust-timer]

Finished benchmarking commit (b588641): comparison URL.

Overall result: ✅ improvements - no action needed

@rustbot label: -perf-regression

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.3%	[-0.3%, -0.3%]	1
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	2.3%	[2.3%, 2.3%]	1
Improvements ✅ (primary)	-1.7%	[-2.1%, -1.3%]	2
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-1.7%	[-2.1%, -1.3%]	2

Cycles

This benchmark run did not return any relevant results for this metric.

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 630.462s -> 629.598s (-0.14%)
Artifact size: 316.63 MiB -> 316.67 MiB (0.01%)