It's directly related to a MP3 id3v2.3 tag. There's an app called Serato that creates it's own data placed in a GEOB (General encapsulated object).

Let me explain:
Here's our string:

Decode the value to get the binary output. This tool proves useful: http://base64-encoding.online-domain-tools.com/

COLOR:
AQFDT0xPUgAAAAAEAJmZmU
First 8 chars are: ..COLOR. (Hex: 01 01 43 4f 4c 4f 52 00)
The next 8 chars are: ........ (Hex: 00 00 00 04 00 99 99 99)
The hex value "99 99 99" is the actual colour.

The next step is where I'm stuck and what the bounty is for. You can find the start of a CUE by finding the end of a colour value.
Hex: 43 55 45 (CUE). After this value, there should be values of Time, Colour, Text(START)

The difficulty is decoding the individual items (CUEs), not the object itself.