The first bank of color RAM is bad - the write/read test has come back mismatched
5555 - expected
DD - RAM bank 0
55- RAM bank 1
Color RAM is a pair of 6264 SRAM, generally Toshiba or Sony slimline in my experience. The bad one IIRC will be the bottom one, not sure where it is on your board but I seem to remember it's usually down near the edge connector
It could also be the associated custom, but I've had colour RAM faults on 3 boards now and on all 3 (all of which had Sony slimline RAM) it was the RAM itself. All Bank 0 too IIRC
Generally the screen goes all 1 colour when these fail too, yours so far just has the big red line at the top