Birthday flowers for Lucy , fresco. photo later

Painting this was frustrating as I soon saw that the spring flowers needed clear yellows, blues ,pinks, and I had only earth colours that I could rely on being lime tolerant. How do I test for lime tolerance? If it is OK, How long will this be safe: for 1000 years? 5 years? Who knows? Are frescoes OK out of doors in GB? Is it advised to protect an outside wall with something like an overhanging porch?