Generally, the answer is no. I understand if you take a freshly cut piece of wood and let it sit out in the sun and weather for a year or so, it will darken in color. However, when we are talking about drywood termites consuming and leaving droppings (pellets) behind there are too many variables to determine this.
Too many times another company visits a property informing the owner of an infestation that is old or new by the color of their droppings. Which should never be the case.
Let’s take a closer look at a piece of wood from the inside. We all know that there are rings inside that piece of wood created by the amount of moisture that tree had received over its life time. Wood grain is a longitudinal arrangement of wood fibers. Depending on the type of tree, those rings/fibers can be very different in color. Not to mention all the limbs that grow off the tree which end up being knots in the wood when milled, and the heart of the wood which is in the initial growth of the tree.
Depending on where the infestation is located, droppings can look all the same color, like when the termites consume pine, ash, birch, poplar and maple. When Drywood termites consume dark color wood like oak, redwood, mesquite, cherry, etc., their droppings can have different color droppings from these fibers consumed. Most homes are built with Douglas Fir, which is a softer wood and can be lighter in color, but most of the Douglas Fir material that is used for framing home is #2 grade, which will have more knots and hearts in the wood. Douglas Fir #1 grade will have less of these knots and hearts, but generally are more expensive, this is why builders use #2 grade lumber for framing.
Droppings/Pellets that are excreted in subareas and attics where their is a lot of dust and dirt that collects can mask droppings, but will not change the color of them.
The most effective way to determine if the infestation of Drywood termites is old or new is remove or mask the droppings/pellets. Do not determine if the infestation is old or new by the color of the droppings.