I want to fill and outline polygons by using a field that contains HEX codes as a string, e.g. #99d594, as well as set the fill opacity to 25%.

I'm able to set the colours with the right field through the Data defined override option (Data defined override button > Field type: string > select field):

data defined override

Having the fill and outline colours set, I want to set a 25% opacity to the fill. But it displays at 100% opacity even when the opacity is set at 25%.

Below the opacity setting doesn't reflect on the map when I set the fill colour with a string field:

before and after colour defined by string field

How do I ensure that the opacity reflects when I define a fill colour with a string field?




  • Have you considered handing rgba values, which include transparency?
    – Erik
    Jul 1 at 12:52
  • @Erik, our client works with HEX codes, but I will look into the possibility of rgba values - thanks for mentioning it!
    – CJL
    Jul 1 at 13:06

2 Answers 2


If you don't want to add transparency to the HEX-code and have the value static or in a field, you can use this expression :

with_variable('fill_color', '#99d594',  -- replace with color field
with_variable('transparency', 25,  -- percent
    color_part(@fill_color, 'red'),
    color_part(@fill_color, 'green'),
    color_part(@fill_color, 'blue'),
    @transparency / 100 * 255
  • this works perfectly, thank you!! Going to try to add an image of my result somewhere below here...
    – CJL
    Jul 1 at 13:51

Ah, the more you research:

You can add transparency to HEX-codes by adding two leading characters as per this list: https://gist.github.com/lopspower/03fb1cc0ac9f32ef38f4

E.g., a leading 80 will give you a transparency of 50%, so '#80000099' results in a transparent dark blue.

enter image description here

So the code for your example would be '#BF99d594'.

  • I also came across a post that mentioned adding two leading characters, but was hoping not to fiddle too much with the client's data. But the link that you've shared is very useful though, thanks!!
    – CJL
    Jul 1 at 13:48

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