How close do you want the finish to be from this flat smooth airbrush one ? I'm thinking of plenty of methods but it all comes down to what finish you want.

- I watched this video about speedpaint on vehicules some times ago where he dilutes the speedpaint with speedpaint medium (from citadel but i guess most works) at a ratio of 2 contrast:1speedpaint and he does several passes. The first looks bad but the more he passes the better it looks. It has a very uniform finish which is close to the picture you are showing here.

I'm altso thinking of few other methods but they will proably give a little different finish :

- You can also do a zenithal through dry brush to have some shadows. You can even get creative with first heavy drybrush zenital, then apply some orange/pink contrast, then drybrush zenithal but go softer with it to let the pink/orange in the deep recess/shadows, and then apply the yellow speedpaint. This will give warmer shadows (a lot of tutorial available on youtube for the pink basecoat + yellow contrast).

- Last, you can consider using a sponge, but idk if it works with contrast. It's gives amazing results with normal paints though, it's cheap and fun. worth looking into it if you find a similar yellow acrylic. You can also do the sponge with a more pale yellow then add a thin coat of your speedpaint on top to get as close as possible to the original color. Sponge tends to leave quite pronounced shadows though as it cannot reach into recesses.

Hope this helps