The four colors stand for diversity.
Four hearts symbolically show that racism and misanthropy can only be countered together and with a heart. That you have to convince with arguments and patience, not with counter-violence or aggression. Even if that is sometimes difficult.
This can be different skin colors or other external characteristics, cultural identities, social or geographical origin or other physical or psychological differences between people.
All four hearts together form a unit - the ShowYourColours symbol.
No heart can be missing, otherwise the symbol would not be complete. Just as humanity is one whole. We all belong together, no one should be missing, no one should be excluded.
There are no graphic separators between the hearts. As a symbol that by nature there are no national borders. These are man-made.
No human owns land on this planet. The earth and thus the entire country and thus all countries in the sense of states belong to all people - and incidentally also to all animals and plants.
Well, all living beings - we often forget that too.