- some others, often with military roots (FS595, British Standard, …)
Pantone has different charts for paper/textile prints etc. RAL is mostly used for paint. It's common to have RAL codes on spray cans or wall paint buckets here in Europe.
There are tools to approximately convert RGB (and HSL and others) to these colors, eg. http://rgb.to/. But since the color models and intended use are different, there are some colors with no equivalent.
It's definitely not as simple as RGB. Displays use an additive color model (you start from black and add more light), whereas paints use a subtractive color model (you start from white and add pigment).
The standard model for subtractive color is CMYK -- cyan, magenta, yellow and black. Calibrating RGB displays to offer a reasonable preview of CMYK color is quite tricky due to the completely different color space and dynamics.
Wall paints are an additional step removed because you can't buy them in CMYK, and the vendors don't provide a mapping from their private color names into a standard CMYK space.
Neither is a good fit of describing colours in the real world, as they're dependent on the output device (in case of CMYK both the printer and the paper change the resulting colour). So a mapping of paints to CMYK or RGB would be rather meaningless.
That's certainly true. But CMYK would be more useful because the commonly used CMYK spaces can represent a color gamut that's closer to the range of shades in the actual paints, whereas the commonly used RGB spaces are too limited. (A regular color printer can print a substantial range of colors that are aliased when represented in sRGB, i.e. you can't distinguish them on screen unless the preview is adjusted to compensate. This also happens the other way: many on-screen greens can't be printed without extra inks.)
I am currently working on a feature which will show the closest matching Pantone colors to the captured color (which is calculated in the LAB color space for high accuracy). Would that fit your use case?
I haven't looked at a paint can in a while, maybe it's as simple as rgb?