This is one of the commonest pansies although in many cases the plants that one finds are garden escapes of Viola 'Hortensis' that look very similar but can be recognised by the red/purple upper petals. They often also have larger flowers.

The true Viola tricolor comes in a variety of colours and shades but (almost)completely yellow ones are rare. These yellow ones could be backcrosses from Viola x contempta to V. tricolor to make the flowers larger but still have the typical V. arvensis colouration.