Transparency

The value of this parameter nominates, in hexadecimal rrggbb format, a colour to be rendered as transparent within the object. This has the effect of making all regions that match the nominated colour completely hidden, with other windows and applications visible "underneath". If this parameter is unspecified or invalid, no colours are nominated as transparent.

Values: any string containing a 24 bit hexadecimal value, where the 8 highest-order bits denote the level of red in the nominated colour, the 8 middle-order bits denote the level of green in the nominated colour and the 8 lowest-order bits denote the level of blue in the nominated colour