The size of bubbles represents number of voters, the color is mixed from basic colors representing each party.

ČSSD: 2 times more than both ANO and TOP09+ODS
ANO 2011: 2 times more than both ČSSD and TOP09+ODS
TOP09+ODS: 2 times more than both ČSSD and ANO
ČSSD and ANO equal: 2 times more than TOP09+ODS
ČSSD and TOP09+ODS equal: 2 times more than ANO
ANO and TOP09+ODS equal: 2 times more than ČSSD
ČSSD, ANO and TOP09+ODS equal
The colors are stressing more the differences (otherwise would be more white-ish)