Is Sciton Halo laser safe to do when I have olive skin tone and melasma? I'm worried the melasma may become worse.

Halo is an excellent choice for darker skin types and hyperpigmentation, including melasma... with the right settings.   Please make sure you see an experienced provider that is aware of different settings for certain disorders and of course skin types.   Halo is less likely to leave footprints on the skin post laser treatments in darker skin types.   As others have said however, melasma is a life long battle which requires maintenance before and after treatments including sunscreen, sun protection, at home skin care products that decrease pigment production, etc.   So the laser is a maintenance treatment, not a cure.  

halo can be used but has to be done with low settings and combined with skincare/peels like enlighten.  most lasers however can cause PIH or Melasma to worsen, either with frank bad luck or without skin prep. 
Hyperpigmentation from any type needs a combination approach of peels like cosmelan,  lasers like clear and brilliant and aerolase or laser genesis, radiofrequency like venus viva, and constant skin care and sun protection.  Bimontly facials with silk peel dermalinfusion is essential to hydrate, exfoliate and infuse vitamins and antioxidants into the skin.  If you have acne you can do additional treatments and peels to get more improvement.  I suggest a formal consultation with an expert in lasers and peels. Best, Dr. Emer.

Any skin improvement should be performed with caution and only by experienced providers in patients with melasma. It is imperative that any treatment only be done when the patient can be strictly out of the sun for at least 2 weeks before and after, an appropriate prescription / non-prescription skincare regimen has be started to pretreat and then restarted on day 3 after treatment to reduce chances of hyperpigmentation. We also test patch all our melasma patients so we know that the settings we have chosen work with their skin.