I agree with previous postings that the Medieval world was generally more colourful than most people realise. I am sure most castellans would not have missed the propaganda/morale value of painting hoardings with their heraldry (many pieces of which would be prefabricated and stored for ease and speed of assembly in time of conflict). These would almost certainly be concentrated around the main entrance etc.
Painting was also an effective method of resisting rot and adding a measure of fire resistance.
It should also be mentioned however that this bravado probably had a price. Attacking archers would have used any visible fixed point to aim at. A conventional cruciform arrowslit enhanced the field of vision through the horizontal openings allowing defenders to view the target before it entered range. At White Castle, Wales, the slits are off-set (called displaced traverse slots). This has been hailed as a design advance since it still gave the defender the extra vision, but did not provide the attacker with an 'X-marks-the-spot' point to aim at.