If the gems are matched in special form, this will result in summon a Gemling. See this for more information.
After the player cleared a level, the Gemlings will gain gems(exps) to leveling themselves up until they hit to max. level(5), the amount of the gems can be increased by how many gems cleaned in that game. For example, a Grass Gemling will gain 50 gems if the player cleaned 50 green gems in total.
The visual design of all 6 gems were changed after the legacy version 2.1.
After the legacy version 2.8.3, the hue of gems has been tweaked and gained the bold outline from the second gem designs. The shadow on gems also has been changed into three-dimensional bottom shadow from two-dimensional drop shadow.