There are a Few Options
A) Move around the planet
While this is the least energy efficient - and a somewhat strange - option, you could move your colony around the planet throughout the year in such a way that they are always on the border between the light and dark parts of the planet. They will get a decent amount of light, comparable to sunrise or sunset, but they will be least affected by solar flares.
This would be most efficient if your colony orbits the planet, or if there is an ocean large enough for a floating colony to navigate the seas throughout the year.
B) Settle underground
See this poster from National Geographic for a visual of what a colony might look like
Lava tubes are cave-like conduits formed underground by cooled, hardened lava
after molten rock has flowed through. Scientists say the ones on Mars may be
significantly larger than those on Earth. The interiors of the Martian tubes,
hidden under dozens of feet of solid rock, are protected from cosmic and solar
radiation and fluctuating temperatures on the harsh, dusty surface.
If your future colonist analyze the structures below the surface, using something like this, they may find lava tubes perfectly suited for colonies! And if not - they can still dig to a reasonable depth where radiation won't cause problems.
C) Use radiation shielding
Scientists have proposed numerous strategies that would allow your colonists to build above ground - it just might not be pretty. Consider coating all structures in six feet of soil, or adding thick metal plates - it doesn't take a lot to match the protection an atmosphere gives once you have a magnetic field - and voila! Earth-like protection.
D) Use artificial magnetic fields
If your colonists want to live above ground, in the sunlight, without thick plating, and stay in once place, this is your final option. It is plausible that by the time your colonists arrive, humans will have figured out how to make cheap magnetic fields - which, if strong enough, are all you need to keep out the radiation from flares.
Also note that if you want croups outside the colony, on the surface, this method would work best.