Accessory pigments are also photosynthetic pigments, like chlorophyll- $b$, xanthophyll and carotenoids which are not directly involved in emission of excited electron, but they help in harvesting solar radiation and pass it on to chlorophyll- $a$.
This pigment itself absorbs maximum radiation at blue and red region. So the chief pigment of photosynthesis is chlorophyll and others (i.e, chlorophyll- $b$ xanthophyll and carotenoid) are accessory pigments.