Will the natural blue color turn brown or fade?

It can, and this is one of the more challenging areas of natural color formulation. Spirulina-based blue — the most commonly used natural blue — is sensitive to both heat and acidic conditions. In a heated or acidic environment, it can shift toward green or brown rather than maintaining a clean blue. The practical ways to mitigate this are to add the color as late in the process as feasible to minimize heat exposure, keep the pH of your system as neutral as possible if blue stability is a priority, and validate the finished shade after your full process rather than evaluating it before heating. Managing expectations is also important — achieving a stable, vibrant blue with natural pigments is genuinely more difficult than with synthetic options.