Ok, I found my inspiration in this key (Ruwenzori Expedition 1934-35 vol. II. No. 3 - Fritz van Emden) :
Graphomyia R.-D.
1(18). Pattern black and yellowish grey. Thorax with or without three broad black longitudinal vittae which may be connected and interrupted transversely[...]
2(5). Femora yellow, sometimes brownish apically. Hind tibia without a submedian posterior bristle. Interfrontalia quite bare between the two rows of frontal bristles.
3(4). Eyes bare. Palpi yellow. Hair black. Thorax with three broad black dorsal vittae of almost uniform width. Tibiae and often tip of femora brownish...........
eustolia Walk.
4(3). Eyes densely haired. Palpi black. Hair yellow on pleura. Thorax with traces of three brownish dorsal vittae. Tibia and tip of femora not darkened............
aurata Mall.
[...]
18(1). Pattern black and greyish to dark bluish grey. Thorax with four black vittae in front, the submedian ones not reaching scutellum. [...]
Maybe it can help...