Clearer explanation of [colorize with alpha

doc/lua_api.txt

@@ -361,9 +361,9 @@ Colorize the textures with the given color.
 it is an int, then it specifies how far to interpolate between the
 colors where 0 is only the texture color and 255 is only `<color>`. If
 omitted, the alpha of `<color>` will be used as the ratio.  If it is
-the word "`alpha`", then the alpha of the color will be multiplied with
-the alpha of the texture with the RGB of the color replacing the RGB of
-the texture.
+the word "`alpha`", then each texture pixel will contain the RGB of
+`<color>` and the alpha of `<color>` multiplied by the alpha of the
+texture pixel.
 
 Sounds
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