The worst part about web colour is that it's not even consistent. If you draw a PNG containing a rectangle with a given colour on to a page with background colour of the
exact same RGB values, then it can look different.
Here's an example: https://incoherency.co.uk/interest/colour.html
And here's a screenshot of how it looks on my browser (Firefox 99.0, Ubuntu 20.04 LTS): https://img.incoherency.co.uk/3812
The square is a different colour to the page background colour despite having the same RGB value (#0cf4c7) but they look different. No amount of changing the colour mode selection in GIMP can fix this.
I opened the screenshot in GIMP and used the colour picker tool to see what colour my #0cf4c7 has turned into, and in the screenshot image it is #67f1c7.
Strangely, when I draw the screenshot in the browser, its colours stay the same, so obviously there is something you can do to the PNG that will make it render the colours you chose.
Here's an example: https://incoherency.co.uk/interest/colour.html
And here's a screenshot of how it looks on my browser (Firefox 99.0, Ubuntu 20.04 LTS): https://img.incoherency.co.uk/3812
The square is a different colour to the page background colour despite having the same RGB value (#0cf4c7) but they look different. No amount of changing the colour mode selection in GIMP can fix this.
I opened the screenshot in GIMP and used the colour picker tool to see what colour my #0cf4c7 has turned into, and in the screenshot image it is #67f1c7.
Strangely, when I draw the screenshot in the browser, its colours stay the same, so obviously there is something you can do to the PNG that will make it render the colours you chose.