In Latvian Lieldienas is a compound word which literally means "big days": liel-(as) "big" + dienas "days". I'm not certain, but I assume this refers to the fact that the amount of sunlight is increasing, and the "day" is now "bigger" (i.e. longer) than it was in the wintertime.
In any case, Lieldienas was a "big" celebration, and (like Ziemassvētki — Latvian Christmas) was celebrated for three full days (and, in some areas, for four).
One of the older traditions associated with Lieldienas is building a swing (preferably on a tall hill), and swinging on it as high as possible. This appears to be a magical tradition; some say that by swinging high in the air, it encourages the sun to keep rising higher and higher in the sky as spring progresses.
Colouring eggs appears to be a more recent tradition, but one which everyone enjoys. Most commonly Latvians would colour their eggs by boiling them in water which contained a large quantity of dry onion skins. This could produce a variety of colours, depending on how long the eggs were left in the water. A short immersion produces a light yellow, a longer one a golden brown, and a very long immersion — a deep, ruddy brown.
Another technique is to take a needle and scratch a pattern into the surface of the dyed egg. This takes a lot of time and patience, but can achieve some delightful results:
*Easter Sunday is the Sunday following the Paschal Full Moon (PFM) date for the year. In June 325 A.D. astronomers approximated astronomical full moon dates for the Christian church, calling them Ecclesiastical Full Moon (EFM) dates. From 326 A.D. the PFM date has always been the EFM date after March 20 (which was the equinox date in 325 A.D.). (Definition is taken from Easter Dating)