Quick guide to getting rid of that irritating tash line
I say apply a good face primer, then foundation ,the way you apply moisturizer: let it set (or dry). Then buff it off with a dry brush or sponge. If you also wear powder or a powder foundation, after application, lightly mist your face with a toner to settle the powder. You can just let that be, or pat it dry.
Choose a translucent foundation with a pink, yellow or orange tint, depending on your skin tone. Pink works best to cover blue shadows on paler people, while yellow works for medium skin tones and orange for dark skin tones
If you need more cover choose a concealer with the same tint as your foundation that is a couple of shades lighter. Stipple the concealer onto the shadow, then blend it in with an applicator.