Senses veiling.
Perhaps the veil fallout would temporarily 'paint' the caster the same colour as his surroundings, maybe including floral wallpaper, poster details on his face etc or just the same colour all over i.e. bright blue or similar.
Alternatively, the casters face or image could be projected to all tv screens in the area, or everything they say is broadcast on the radio.
Mental veiling.
Everyone he was trying to hide from is suddenly convinced the caster is there and is extremely alert to any sound or movement. Or perhaps the casters thoughts can now be heard as if they are speaking.
Light veiling.
As Papa Gruff said, perhaps the caster could suddenly radiate light, or perhaps the shadows disappear, maybe the lighting completely inverts and light areas are now pitch black and dark areas are now blinding white?
Sound veiling.
Perhaps now every sound they make is magnified, pounding hearts, rustling clothes and ticking watches can be heard clearly.
Whatever inverts the intent of the spell, and the method by which it's cast in an interesting way for storytelling. If you don't want the veil fallout to ruin their plans, perhaps those alerted guards are now easy to distract, perhaps the inverted light can be used to their advantage with some quick thinking.