Every creature is a one drop.
But everything else... can be anything!

Life Gain - W/B/G (medium?)
Goblins/Sac - R/B (aggro)
Sacrifice/Value - B/G (control)
Removal/Revival - B/W (control)
Spells - U/R (control)
Soldiers/Humans - W (medium)
Equipment - R/W (medium)
+1/+1 Counters - W/G/U (m/control?)

?? Merfolk - U/G (medium?)
?? Elves - G (aggro)
?? Mill - U/B (aggro)

2Clrs R B U W G
R x x x
B x x x
U x ? x
W x x ? x
G x x x