Next draw yellow after red leads by five

An urn holds $140$ balls: $20$ of each of the seven rainbow colours. Balls are drawn one at a time without replacement. You are told that among the first $70$ draws there were exactly $5$ more red balls than yellow balls. What is the probability that the $71$st draw is yellow?

$\tfrac{5}{28}$. The condition only involves red versus yellow, so by symmetry each of the other five colours is still $\tfrac17$ likely on the next draw, leaving $\tfrac27$ for red plus yellow. Exactly $5$ more yellows than reds remain among the $70$ balls left, so yellow exceeds red by $\tfrac5{70}$; solving gives $\tfrac{5}{28}$.