hey frankamato!
i have been using dior skinflash radiance booster pen in candlelight for a while now and really like it. it is really, really subtle. it is a concealer, but also not obvious at all and really makes your skin glow. i will put it on the bridge of my nose, under my eyes for circles, under my brows. i just think it makes you look glowy and polished. they sell it at sephora, so you can try it in the store first.
i love trisha's suggestion of clear mascara! if you are just trying to perk up your face, that would do it without adding any color, and i think it would be really subtle and nice.