it's bigger brother FCPX has such an effect for video.-
no plug-ins for the actual version of iMovie.
for sure, when double-click a clip in iM, the Inspector/Video offers some basic color-corrections/-manipulations, such as moving the white-point.
your examples are a bit more tricky, due to some colors are not affected - ex #1 the sky stays blue allthough the color-temperature is set to more 'warmth'.
ex #2, the guy, is simpler: raise brightness, add warmth, raise saturation ......