Well, actually it's fractional values. I find the following table handy when attempting to convert programs written for those sorts of monitors.
| Colour # | R | G | B |
|---|---|---|---|
| 0 | 0 | 0 | 0 |
| 1 | 0 | 0 | 2/3 |
| 2 | 0 | 2/3 | 0 |
| 3 | 0 | 2/3 | 2/3 |
| 4 | 2/3 | 0 | 0 |
| 5 | 2/3 | 0 | 2/3 |
| 6 | 2/3 | 1/3 | 0 |
| 7 | 2/3 | 2/3 | 2/3 |
| 8 | 1/3 | 1/3 | 1/3 |
| 9 | 1/3 | 1/3 | 1 |
| 10 | 1/3 | 1 | 1/3 |
| 11 | 1/3 | 1 | 1 |
| 12 | 1 | 1/3 | 1/3 |
| 13 | 1 | 1/3 | 1 |
| 14 | 1 | 1 | 1/3 |
| 15 | 1 | 1 | 1 |
I don't need to know the remaining 48 (EGA-only) colours too often so I haven't got around to them yet.