I depends, though “small greenish blob” would be a good description. The other answers contain great pictures of plant chloroplasts under a decent quality light microscope. However, plants (and algae) don’t all have the same size of chloroplasts and the chloroplasts can be very hard to see when they are small, not just because of size, be also because they appear less green (small size = less light absorption = less green in color).
If you use fluorescence microscopy, then the chloroplasts glow reddish-orange in color (very cool, especially when you have swimming algae).
