Colour RAM can be written from unintended address ranges.

[MassiveBattlebotsFan]

Test Environment (required)

• Platform: All
• Core version: Latest development
• ROM version: N/A

Describe the bug
Colour RAM can be written to via addresses $0Fx8.yyyy, where x != $F.

To Reproduce

1. Write bytes to $0Fx8.yyyy.
2. Read the same bytes from $0FF8.yyyy.

Expected behavior
Colour RAM should not be writable at the addresses mentioned above.

Screenshots
N/A

Additional context
None