I want to symbolize several values from one layer using R, G, and B values. So, column 1 would be the blue aspect, from 0-255 based on min and max values, column 2 would be green, and column 3 would be red.

I can't find a way to do this in QGIS 3 without creating 16 million rules. If I make multiple layers with color and transparency, then whichever layer is added last dominates the color spectrum.


You can use an expression to control colour, for example in the Simple Fill of a polygon, click the "expression" button at the right hand side, then choose "Edit":

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Then in the expression enter something like:

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where "red", "green", and "blue" are the field names with the colour values from 0 to 255. Put the names in double quotes as shown. Help on the color_rgb function should show up in the dialog. Apply that and...

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polygons coloured (and labelled, so you can tell) with RGB values from the attributes.

  • Those color helper functions are really helpful. I am trying cmyk so that I can change brightness independent of shade (otherwise everything comes out pastel with my data)
    – user15741
    Jun 14 '19 at 16:21

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