Sketch's Loupe Should Be Offset
These days, I'm totally sold on using Sketch. I've transitioned over from Fireworks for 100% of my professional and personal design work, and while I'm not looking back, there are a few things I think Sketch could improve. One of them is the color-picker loupe.
A loupe is a physical magnifying glass that's been appropriated as a metaphor in software interfaces. In Sketch (and other design/drawing apps), it assists the user in picking colors with the eyedropper tool.
To change the color of the purple star in the example below, a user can click the color box, select the eyedropper and then choose a single pixel from elsewhere in the document. That pixel's color will be used as the color selection.
Because clicking on a single pixel is pretty difficult, the loupe zooms in on the cursor position. This is a good input aid, especially for selecting things like 1px lines.
However, because the loupe covers the canvas, it can obscure the thing the user is trying to target. This usually happens to me when I'm zoomed out and makes me have to scroll the mouse around via dead reckoning for a few moments, trying to land on my target color.
You can see the problem better in this gif -- watch how the loupe totally covers the stars for a moment.
This isn't the end of the world, but I think it could be done a little more smoothly if the loupe were offset from the mouse pointer. The user could still mouse slowly to go pixel-by-pixel, but large movements would be a lot easier.