Japanese armour was not bare metal*, but lacquered, which reduced its shininess. Because it tended to be made of small flat plates and scales woven together, which produce many irregularities and shadows, the individually-shiny pieces don't tend to actually look all that shiny when put together because the individual highlights are just too small. On top of that, a lot of the materials used on the outside aren't shiny to begin with. Here's a very shiny example
, zoom out and it's basically matte. Here's another
, with great speculars on the bare plate on his arms, but all the speculars on the laced parts aren't very noticeable and don't help convey the form.
In other words, while some form
highlights would be good in the sprite to give it a better sense of form/3Dness, I don't think speculars are appropriate. Instead, I think it would work better to use lighter colours for the lit parts, and to have a less-frontal light source on the chest piece, so it doesn't look so pillow-shaded. The colours in CFK's edit are good, shininess aside.
The character's arms don't seem to be very well protected. Unless they're an archer, they'd probably have gauntlets something like the second photo I sent, rather than gloves/mittens - the fingers would likely be bare, for finer control of whatever weapon they used, the back of the hand protected by a plate attached to the arm protector. Wikimedia Commons to the rescue
* European armour was also not actually shiny, it tended to be matte, even the smooth plate armour that we most associate with "knights in shining armour". Most shiny armour in museums was either purely decorative, or polished to that level to look pretty by uninformed collectors/curators who thought all armour looked like the decorative pieces and the matte look was just from ageing. Something to keep in mind if you want a degree of realism in your future designs.