Sapphire and ruby are the safest picks for a ring you wear every day. Both rate 9 on the Mohs scale, one step below diamond's 10, so they stand up to the knocks and scuffs of normal life far better than most colored stones. Emerald is a different story. At about 7.5 to 8 it is softer, and it is more brittle, so a sharp blow can chip an edge.
None of this rules emerald out. It simply means the gem you love should shape the setting you choose, and that the setting matters more for a softer stone than it does for a sapphire.
If your heart is set on emerald, choose a mounting that covers its edges. A bezel setting wraps the stone in a rim of metal and is the most protective option, and a border of diamonds around the outline also shields it from side knocks. Avoid tall, open heads that leave the gem exposed; a lower mounting sits closer to the finger, where it meets fewer bumps.
Prongs still work well for a tougher gem. Sapphire and ruby sit happily in four or six prongs, and six give a firmer hold if the ring will see hard use. Whatever the stone, ask how much of its edge is left open, because that edge is where a colored gem is most likely to take a knock.
A gemstone can take the center or play a supporting role. A colored center ringed by a diamond halo, or flanked by diamond side stones, puts the color up front with white sparkle around it. A diamond center with small gemstone accents along the band or under the head is the quieter version, a flash of color you notice up close. If you are torn, that second route is the safer bet for wear, since the stone taking the most knocks is then the hardest one. Look at halo settings to see how a frame of small diamonds changes the look of a center.
Metal shifts how a gem reads. White gold and platinum keep blues and greens cool and crisp and give a ruby a bright, clean frame. Yellow gold warms the whole ring and lends a sapphire a richer, more traditional feel. Rose gold softens everything and suits warm or pinkish tones. If you are unsure, picture the ring beside the jewelry you already wear most, since an engagement ring has to live with it.
For finished ideas that combine color and diamonds, browse gemstone engagement rings for women.