That slight brown shading you may see to the right by the edge is tracked in blacktop sealer. Haven't seen anything to shake blacktopsealer.

post another pic after a week.

nice job btw-

Google "asphalt chemical transfer" and you will get this article or a variation of it. Our janitorial company had an account with this problem. The blue carpet discolored quickly and I wish we knew then what was causing it. We could have defended ourselves better and offered good advice.
Asphalt chemical transfer:
Yellowed carpet from Asphalt - Asphalt coating may be walked onto the carpet (and even onto vinyl tile) from driveways and parking lots and turn the carpet yellow. Since this is being tracked in from the outside, it is most noticeable near the entry areas. This is most common after repaving or sealing the asphalt, especially in the summer with elevated temperatures.
This is most commonly a problem on blue and light gray carpet.
Yellowing from asphalt track-in is virtually impossible to remove. Asphalt coating and sealers are coal tar based materials, which are yellow when highly diluted in solvent. Unfortunately, the solvents required to totally remove these materials are also strong enough to delaminate the carpet. Whenever a customer asks for your advice on replacing carpet and has a parking lot, advise him or her to avoid blue and light gray

The BENE-CLENE web site adds the following "If the problem is fresh, apply TLS 2000 and do your normal cleaning followed with a Brown Out flush at about 2 ounces per gallon. If this fails, prespray Citrus APS™, scrub (if loop pile) and clean. Sometimes, adding Pro’s Choice Energy to your prespray will help. Use very long floor mats (at least 12 feet) to reduce the problem. The problem, however, will not permanently go away".

Asphalt,
I did an apartment with DS, did not get desired results, hey asphalt is nasty, the guy worked on a paving crew and left his boots on in his house!

Went to a JanSan company that also sells products for detailing cars. The chemistry in the car care formulations is designed for road issues. So used the Crystal Foam Shampoo with good results, it brought it from black to light grey.