My go-to thread for almost every project is the Dove (2600) grey Aurifil thread. It blends with pretty much every fabric.
The 80 weight Aurifil thread is incredibly fine, perfect for English paper piecing, needle turn applique and those times you don't want your stitches to be seen, such as when binding or closing up gaps in bags or cushions!
These is 280m on a wooden spool.
Made in Italy. 100% Cotton.