yellowish green sounds more like a discharge from an infection than from a plug. plugs are generally like egg white tinged with blood. i'd request a urine test in your position, water infections are very common for a lot of pregnant women and are easily treated with anti biotics
This is what i found on the internet!
What Does the Mucus Plug Look Like?
The mucus plug often looks like a jelly-like chunk of discharge that is clear, slightly pink, or tinged with a small amount of blood. Sometimes, instead of a jelly-like chunk, in some women the mucus plug looks like stringy mucus or a sticky discharge.
While blood in the mucus plug can be normal, the amount of blood is generally a spot -- no more than a teaspoon or two. If you have more blood than that, contact your healthcare provider.