Frogs look healthy to me. Color sometimes has to deal with environment or moods and not necessarily indicates a problem.

For filtering you can go with something as simple as one of the low height aquarium foam filters and a small air pump, or maybe a small internal water filter that can work in low water levels. Myself prefer one of Danner's Supreme Ovation models; but unsure if that is available at your location.

Once you get the filter installed; continue the water changes for 4 weeks to let filter get established with beneficial bacteria. Then do a 20-25% water change weekly or adjust schedule as required, to maintain nitrates below 50PPM (ammonia and nitrites should be zero). Good luck !