It's just an unfortunate combination of small WinSCP icon (as you have "small" task bar icons enabled) and your task bar color.
Not sure if this is a res problem, or just the icon is exactly as it should? Something sharper would be nice for aesthetics reason, nothing more. :)
What resolution do you need? There's 256x256 icon.
Please post a screenshot.
Big thanks for your work with WinSCP.
Quick note - it would be great if you could update the icon sets with high resolution versions (and perhaps something simpler looking to look more modern). The current one looks a bit unappealing and blurry relative to other icons (especially when you use small taskbar in Win 10).
All the best!