Monstrous extremities will not work with the ring of seven lovely colors. You can only have one polymorph spell on at a time. You can only be affected by one or the other.
The ring lets the user use beast shape IV to transform into a songbird. Both beast shape and monstrous extremities are transmutation(polymorph) spells.
You can only be affected by one polymorph spell at a time. If a new polymorph spell is cast on you (or you activate a polymorph effect, such as wild shape), you can decide whether or not to allow it to affect you, taking the place of the old spell. In addition, other spells that change your size have no effect on you while you are under the effects of a polymorph spell.