Did you already have yellow tulips in your garden? Do you plant the newer bulbs (at the right time of year) nearby?

Try planting some in a tub next year and see what happens.

are the new 'yellow' ones in the place where you know you planted the other colours or are they in close proximity to them? if near it could be they are dug up by animals soon after planting .
Its unlikely to be due to anything with your soil.