Great image viewer application! Not too complex and straight to the point!
1) I really like the color picker tool but have 2 suggestions that might make it better:
a) A setting to be able to anchor or dock the color picker in different corners of the main window (Top Left, Top Right, Bottom Left, Bottom Right) by default.
b) A new field in the color picker that also records the X and Y coordinate that you clicked on. It could be useful if you are trying to find that location in the image again.
c) When right clicking on text in color picker, have option to copy All values (RGB, HEX, CMYK, HSL and newly recorded XY coordinate, see above) to clipboard. This could be executed as a comma delimited list and with or without headers for example:
X, Y, R, G, B, HEX, C, M, Y, K, H, S, L
256, 325, 32, 67, 99, #204363, 0.68, 0.32, 0, 0.61, 209, 0.51, 0.26
or just
256, 325, 32, 67, 99, #204363, 0.68, 0.32, 0, 0.61, 209, 0.51, 0.26
2) Add a magnification window (maybe dock-able) that would display the part of the image where the cursor is at, at a higher magnification (1.5x, 2x, 2.5x, ... you get the idea). Maybe the magnification setting and default dock position for the window could be set in the settings window.
Keep up the good work!