Here's some information about that from my book, The Piercing Bible to answer your question:

Retainers and various jewelry alternatives are available to camouflage your piercing, though certain spots can be disguised more readily than others. Unfortunately, the most invisible retainers are unsafe to wear until after you are healed.

also:

Nostril Piercing: Concealment
After healing, if you need to conceal your piercing, you can wear a tiny, flat disc that has been painted with skin-tone nail polish. See “DIY Retainers,” page 248, for details on the technique. Another option is a nostril screw topped with a very small dome or ball of flesh-colored acrylic. These can be used for fresh piercings if they meet the safety requirements for minimum size, implant-grade post material, a custom fit, and the ability to withstand the heat and pressure of sterilization.

Clear glass and quartz nostril screws are made for concealment, but they are fundamentally unsuited to a healing piercing since the shape cannot be customized. Use
caution even when trying them in healed piercings, as they can be fragile, and if they don’t fit well, the inflexible material may irritate your piercing.

Retainers in high-tech, inert plastics are also available for post-healing concealment. The plastics are more forgiving than the harder materials, and they are not breakable. Depending on dimensions and design, they may not stay in place well.

Sincerely,

Elayne Angel, Author
The Piercing Bible--The Definitive Guide to Safe Body Piercing
Medical Liaison, Association of Professional Piercers

[email protected]
http://piercingbible.com/
http://www.facebook.com/elayneangel
http://twitter.com/elayneangel
http://www.linkedin.com/in/authorelayneangel