I would name this congenitally blind person as a project.
Congenital blindness is a form of visual impairment wherein the afflicted person has absolutely no idea of what any colour looks like, let alone the colour yellow. However, man, being an evolutionarily advanced creature, has other well-developed senses that respond to external stimuli. One such sense is the gustatory sensation or sense of taste. The sour taste of lemon and other citrus fruits like sweet lemon (commonly known as Mosambi) is the best stimulus that can help the blind person imagine what the colour yellow would look like if he were able to see.
If the project has a sweet tooth, I would serve him or her a lemonade diluted enough to make it palatable. On the other hand, if he or she likes the acidic taste, tamarind or unripe tomatoes would be the best fit.
Moving one step ahead, I would also delve into the personality traits and gauge the behavioural responses of the project when presented with situations that test patience and confidence. For instance, I would try to know if the project has ever been bullied by friends. If yes, I would associate his or her feeling of annoyance with yellow colour.
However, I think it would be unfair on my part to not explain the positive connotations of this colour. After all, the project deserves to know the brighter side of life too. So, I would expose the project to sunshine and ask, “Does the warmth of the sun rays make you cheerful and optimistic?” Moulding my voice to sound enthusiastic and pleasant would help translate feelings into colour.