I thought out-of-gamut wasn't supposed to occur with RGB files or in InDesign.
@Kaatie – why did you think so?
The standard for web applications is still sRGB.
And that means all colors defined can fall in or out of this color space.
A green color defined as 0|255|0 clearly is not inside sRGB. There are numerous RGB color spaces. Neither of them would support all RGB colors you could type in. Or if you would find one that support your specific color, it would not be applicable to web design.
How to solve this:
just live with a duller color. Change your color to the next most brightest green color possible in sRGB.
You could use e.g. PhotoShop for that purpose.
When Export to JPEG are you select Color Space : RGB?
As far as I know, the gamut warning is simply showing you the nearest CMYK equivalent to your chosen RGB, in the document working CMYK profile. If the output is to be RGB you can ignore it.
as Peter says – everything in RGB, here sRGB, but don't forget the
Transparency Blend Space.
Of course R0 G255 B0 is in-gamut in its own RGB space. But more important:
this very vivid green, as defined in sRGB, will be shown (almost) correctly on
calibrated standard monitors, which have primaries near to sRGB (opposed
to wide gamut monitors).
Best regards --Gernot Hoffmann
Click on image for sharp view. It's 24-bit PNG.
and exporting it as a jpeg with a duller colour.
When you export to JPEG is the color mode RGB and are you embedding the RGB profile? Also when you look at the JPEG in Photoshop make sure Proof Colors is turned off.
I thought out-of-gamut wasn't supposed to occur with RGB files or in InDesign
The out-of-gamut warning you see in an InDesign swatch is relative to the document's assigned CMYK profile's gamut.
When you make a new document and choose Web intent the default swatches are RGB colors and the transparency blend space is RGB, but there's no document color mode in ID the way there is in AI or PS.
With Web intent you can still make CMYK colors and output to a CMYK device and there's a document CMYK profile, which defines what's considered out-of-gamut.
If you export to RGB with a profile, you shouldn't see any color change, here's what I get with 0|255|0 at 85% transparency: