Blue Palo Brea,, looks just like the Palo Verde except its thornless and a little darker.. cercidium floridum,, is that what your thinking of?

If it's thornless and has lime-green bark, it could be a 'desert museum', a three-way Parkinsonia/Cercidium hybrid prized for its form, thornlessness, quick growth, and attractive floral display. The blue palo verde (Cercidium floridum) has bluish bark, and does have thorns-lot of 'em. Palo Brea (C. praecox) lime-green bark like the 'desert museum' but has thorns.