Where have you got the hygrometer situated? If it is lower down in the cage, where there is lots of foliage and moist soil in the plant pots, and away from the heat lamps, then 70% is not too high.
Remember, in the environment of a chameleon cage you have to try create gradients. So up near the basking lamp, it should be hot and dry, but down in the plants it should be cooler and humid. Likewise, there will be places that have lots of exposure to UVB, whereas there will also be places that are shady and protected from exposure.
It's all about giving your chameleon choices. The chameleon should be able to decide how to regulate its body: if it's cold, it can go up to bask. If it's too dry, it can move into the moist air in the plant foliage.
That high humidity reading would only be a problem is if the humidity was constantly high THROUGHOUT the cage, and in that case you would notice that the humidity was too high without even needing a hygrometer: if the cage is never drying out between misting sessions or at night, if the water takes very long (more than a couple of hours) to evaporate off the leaves, if the cage smells very dank (swampy), etc.