added documentation for the Color.lerp method

docs/api/math/Color.html

@@ -169,7 +169,10 @@
 
 		<h3>.lerp( [page:Color color], alpha ) [page:this]</h3>
 		<div>
-		todo
+		alpha -- a number between 0 and 1.
+		</div>
+		<div>
+		Linear interpolation of this colors rgb values and the rgb values of the first argument. The alpha argument can be thought of as the percent between the two colors, where 0 is this color and 1 is the first argument.
 		</div>
 
 		<h3>.equals( [page:Color c] ) [page:this]</h3>