Combo colors must not blend in with the map's background/storyboard/video. This is so the approach circles are always visible to the player.Stop using shitty combo colors that you get from the background. Use something bright and/or edit the combo color a higher saturation/luminosity than the base color.
Pretty much any color darker than #80 when converted to grayscale is going to run into issues. Not to mention, kiai and other additive effects are significantly less vibrant at lower RGB values since additive blending adds the RGB value to the color underneath. If you use a black combo color for example, kiai will not work at all because you use 0 for the RGB values, adding 0 to everything. Not to mention, anyone using background dim without a skin force will hate you.
Just delete the color and move on with your life. Nobody is defending how this combo color adds to the song. Everyone is just complaining about the disqualification for something that doesn't seem like a big deal. Drop the AR9 to AR8.9. Change the claps to whistles. Done. I sincerely doubt that there would have been a disqualification if the blue were a better color.
1. I study colour theory and know for a fact that if any colour were hard to see on this bg it would not be the dark blue but actually the orange.Clearly you don't know about how osu! colorization works. Even if the entire background were the exact orange color chosen, the simple fact that the orange is 255,149,43 means that the background when dimmed to the default of 30%, 178,104,30. That's a difference of 77,45,13, which is pretty substantial. The dark blue is just 23,46,83. The difference from a pure blue background would be 7,14,25.
Its common for people to hate on dark blue when they play full dim but that doesn't apply to ranking. Please test on default skin if your skin can't handle dark colours well.
I always test on default skin, and the default skin is very hard to see the dark blue, mainly for the reasons I outlined above. Mappers need to get over themselves and follow the rules. Please note that there is no rule about soft hitclaps or AR9, so those are purely opinionated reasons outlined by the QAT, which are debatable. The dark blue combo color clearly violates the rules.