What is RGB?

In plain language

Video can be sent as RGB or as YCbCr, which separates brightness from colour so the colour can be subsampled. RGB carries full information for every pixel and cannot be subsampled, so it is comparable to 4:4:4 in bandwidth.

Why it matters in your setup

For a PC, RGB or 4:4:4 is what keeps text crisp; a subsampled signal makes coloured text look fringed. For film and television it gains nothing, because the content was mastered subsampled anyway.

The classic trap is the black level. RGB comes in full range (0–255) and limited range (16–235), and a mismatch between source and display produces washed-out blacks or crushed shadow detail — a picture that looks wrong in a way that is hard to name.

What the DR HDMI 8K does with it

The DR HDMI 8K reports the colour space in use on its OLED, and its EDID library includes explicit RGB tables such as 4K30 RGB at 300MHz with and without HDR and BT.2020. In the Dolby Vision section the 444/RGB 10-bit and 12-bit support flags are set separately, so RGB capability can be advertised deliberately.