The idea was to let the ink do the structural work and let the watercolour get loose around it: a pen contour with some weight to it, colour pooling past the edges, and the grain of the paper soaking through. The thing to watch is where the wash crosses the line, and whether the crosshatching survives it.
The blend
Milo Manara — the line.Dip-pen contour creates taut lines of varying weight through crosshatching, fine stippling and dense intricate linework that models form. This is the skeleton. Form is modelled with line, not tone, and the line thickens and thins as it turns.
John Singer Sargent — the wash.Wet-into-wet handling produces translucent washes that pool and back-run via reserved paper whites. This is the colour, put down fast and wet so it pools, blooms back on itself and leaves the paper white where the light is.
Watercolour on cold-press paper — the surface.The paper infuses granulation and blooming edges. A rough sheet, so pigment settles into the tooth and the edges of each wash flower out.
The two artists pull in opposite directions, which is the point. Manara is all control and Sargent is all looseness. The prompt ends on "tints drifting past outlines" and "loose wash held by crisp line": the colour gets to wander because the line is strong enough to hold the picture together anyway. The palette is held to three pigments and one dark ink.
On four models
FLUX 1.1 proGPT-Image-2Muse 1.0Nano Banana 2.1
Flux 1.1 Pro went the most Manara: a glamorous figure in a sheer black dress, drawn in fine nervous pen line, over a hot yellow and orange wash that runs off the edges. A second, smaller figure stands further down the street. It's the boldest version, and the one where the colour really does drift past the line.
GPT Image 2 made the quietest version: a woman in a pale slip dress walking away down a sunlit lane, almost all paper white, with grey-blue washes and very little line. It's more Sargent than Manara.
Muse 1.0 has the most crosshatching. Every shutter, balcony and cobble is drawn, and the washes of ochre and blue sit loosely over the top. A woman in an Edwardian hat and long skirt walks away down the middle.
Nano Banana 2.1 is the most like a travel sketchbook: clean pen line, gentle washes, and a vignette that fades to bare paper at the edges.
Using it
It suits figures and anything with clear edges for the pen to follow: portraits, people in a street, architecture. Flux gives the loosest wash and the most glamour, while Muse gives the most line. If the wash is too timid, push the colour in your subject; the style will happily let it run.
Both artists are named in the prompt. The style page also has a model-neutral version (Franco-Italian pen-and-ink comic illustration and Gilded Age watercolour) for models that won't take names, and an effect-only version with the recipe removed.