Color can be influenced by:
-
scene lighting, global lights & other lights
-
color tinting (see Sprite Renderer’s color property, darkening or alpha?)
-
something going on with the shader or material (do you have the right lit/unlit material?)
-
the colors they’re adjacent to (purely a perceptive difference, N/A here)
In Krita:
- Color management settings
- Color management workflow
- The png export settings, which has its own sRGB
Double check those. My first guess is linear/gamma/sRGB.