The Small Dusty Wave and the Mullein Wave are similar-looking although both are variable with the line patterns they show on the peppered buff background.
Both have a dark spot in the centre of each fore and hind wing and fly at the same time of year. The Mullein Wave is a little larger
(12-14 mm forewing rather than 9-10) and the forewings end in a point/angle like those of the Riband Wave.
Because of the slightly rounded edges to the forewings, these are defined as Small Dusty Wave moths.
A particularly dark individual
Wingspan 19-21mm; UK flight time May-Oct.
This one with somewhat more pointed left forewing looks closer to a Mullein Wave
(Scopula marginepunctata) but is probably another Small Dusty.
This one with a more pointed wing is thought to be the Mullein Wave (but looks very like the Idaea genus of waves).
Wingspan 25-28mm; UK flight time Jun-Sep (southern UK) and Jun-Aug (northern).