score:26
Note that a satirical sketch like this does not necessarily portray the actually participants at a conference. Often, they feature a personification of the nations involved. In this case, as Denis commented, green, blue, white and red are the colours for Russia, France, Austria and England, respectively, derived mainly from their military uniform colours. So:
The man on the left, in green, is Tsar Alexander of Russia.
The standing man next to him is France's Louis Antoine, duc d'AngoulΓͺme. He led the French invasion of Spain.
The man in white is Emperor Francis of Austria.
The man in red is the Duke of Wellington. Note that he is the one saying "You had better not β garde a Toi" - Wellington resolutely opposed the proposed French intervention.
The man in the window is Prince Metternich, the Austrian chancellor and architect of the post-Napoleonic Vienna system.
Edit - As it turns out, Brown University has a high resolution scan of the work.. Check out the link for a better view, but specifically the close ups on the labels identifies all the little figures: