Can you add a photograph please?

As general guidance, yellowing or fading foliage (chlorosis) is a sign of a mineral deficiency; can be nitrogen shortage, although this is unlikely in a legume with their Rhizobium symbiotes. Can be due to a lack of iron, magnesium, manganese, or other rarer elements.
The solution ('scuse the pun) is to foliar feed with a weak solution of something like phostrogen, which contains traces of these elements. Use the watering can rose and get it on the leaves, where it will be absorbed more quickly than through the roots.