Sounds like it. The T commands are text related and rg and k are setting colour in RGB and CMYK. You may be able to figure it out by changing a colour, then looking at what is suddenly bright red or whatever you set. Or by changing the string preceding Tj. When editing, make sure you don't change the length of any objects (use space to pad) as there are hardcoded offsets in a table, usually at the end.

The PDF specification, while long, is pretty readable for this kind of thing. You can download the 1.7 version free from Adobe. Appendix A has a table of commands.