First of all I am really excited about it. Who doesn't want to participate in contests !!! Secondly, there are some things that can be accounted for.

Some acknowledgements(we all know) :

1.Rating and divisions
    Div1-->[1900,9999)
    Div2-->[0,2100)
    Div3-->[0,1600)
    Div4-->[0,1400)

2.There a 4 types of contests held here. 
    a) Type #1: DIV1+DIV2 -->Rating range[0,9999)
    b) Type #2: DIV1-->[1900,9999) & DIV2-->[0,1900) separately on the same round
    c) Type #3: DIV2-->[0,2100)
    d) Type #4: DIV3-->[0,1600)

Now as MikeMirzayanov said, "the number of gray and green participants in total exceeds the number of other participants.". I think slightly modified type of contest may be added.

a) Type #1: DIV1+DIV2+DIV3-->Rating range[0,9999)
b) Type #2: DIV1-->[1900,9999) & DIV2-->[1400,1900) & DIV3-->[0,1400) separately on the same round
c) Type #3: DIV2+DIV3-->[0,2100)
d) Type #4: DIV2-->[1400,2100) & DIV3-->[0,1400) separately on the same round
e) Type #5: DIV3-->[0,1600)

I think this might work.