2 plants - 2 different colors

Personally, I'd do nothing, unless you want to change to soil. Plants aren't uniform, even if the seeds look the same. If you change this plant's soil, consider a smaller container for the interrim and use a well-draining soil mix with lots of aeration in it -perlite or pumice, etc.

If you're looking to keep your plant count up (you want to harvest more than one plant), take a few clones of your successful plant once it's large enough. I posted a super simple, low maintenance cloning process a little while back that I'd recommend to a new grower: DIY: Low Maintenance Cloning Method - Perlite Cloning - Two to Three Weeks - Less than $50. You could have your larger plant flowering out, and once the clones are ready, plant a small carpet of them around your larger plant. They won't grow as large since they'll be planted later in the season, but you'll still get more top colas.

edit: Welcome to GC and congrats on your first post!

 

id recommend to have a little read regarding phenotypes you will be blown away at the amount of variables that these can produce you will get a much better understanding of why some plants thrive but some dont under same conditions in same soil welcome to GC

 

Yeah taking any drastic action right now would be as likely to cause problems as it would be to help...give it some time, and read read read in the mean time...as a previous poster mentioned, the only thing I can imagine causing issues with your seedling is the soil. If it's the exact same soil as it's sister is in, I would imagine you've pulled a different phenotype between the two seedlings.