Yes, the color of the shingles will darken, similar to what it was like when new. Within a couple of years the shingles will start to lighten up as the surface oils begin to oxidize off.
When new, asphalt roof shingles look nice and dark, that's because they are saturated with oil and because of those oils they are flexible and able to withstand expansion and contracting that a shingle endures throughout the heating and cooling of the day. When these oils dry out, shingles begin to look grey and then you'll notice tiny rocks in your gutters.Those tiny rocks are called granules. These granules are the shingles first line of defense from the elements. Granular loss is a clear physical sign that the shingles are aging and drying out heading towards failure. Greying is the first visual sign that the shingles are aging and beginning to dry out. When Greener Shingles asphalt shingle rejuvenator is applied to aging shingles, these super important oils will be replaced and the roof shingles will last much longer.