this is the new palette of the textbox
now use this wbto before your message:
writebytetooffset 0x3F 0x4000048
writebytetooffset 0x1F 0x4000049
writebytetooffset 0x41 0x4000050
writebytetooffset 0x3F 0x4000051
writebytetooffset 0xC 0x4000052
writebytetooffset 0x3 0x4000053
this wbto became BG0 semi-trasaprent
well, to don't have bug load new wbto in the same offset with normal byte after message like so:
writebytetooffset 0x1F 0x4000048
writebytetooffset 0x1F 0x4000049
writebytetooffset 0x40 0x4000050
writebytetooffset 0x1E 0x4000051
writebytetooffset 0x10 0x4000052
writebytetooffset 0x00 0x4000053
screen: