A soldering flux composition comprising: (i) a carrier vehicle comprising a solvent; (ii) an activator component for activating a metal surface for soldering; (iii) a color-imparting component with an appropriate color to facilitate optical detection of flux on the fluxed component; and optionally (iv) a gelling component to control flux rheology. The color-imparting component is utilized to indicate the presence of desired amounts of flux. A component with inadequate flux for reliable soldering can be rejected.