Hmm hard to tell, normally lash eggs are a bit larger and more... fleshy looking. For now I'd keep an eye out for any further deposits (and if you do get any, cut them open and snap a photo or two before disposing of them) and on the behavior of the flock overall.
Eggs at the start of the season are often more pigmented because the (not sure what the technical term is) "spray painter" is full of pigment, and it gets used up through the year, so eggs may overall get lighter towards tail end of laying season.
This is possibly concerning. How large was it...