The issue doesn't happen on v1.x
Normal font weight (possible on hyper 1.4.6):

"Normal" font weight on 2.0

I have tried fontWeight: 'normal', fontWeightBold: 'normal', and fontWeight: '100', but none worked so far
Have you tried reloading fully (CMD+R) after changing this? I think we need to tell xterm to re-render the charAtlas after this setting is changed.
Is "LCD font smoothing" enabled in System Preferences > General? If so, that may be your problem. Disabling the option makes the OS look better, and also applies in applications, so try disabling that.
Check out this issue, it's defaulting the opacity to 0.6 in my terminals too and making it much darker than it should be: https://github.com/zeit/hyper/issues/2827
@iamthemovie He means the font weight, not color.
Most helpful comment
Is "LCD font smoothing" enabled in System Preferences > General? If so, that may be your problem. Disabling the option makes the OS look better, and also applies in applications, so try disabling that.