The big blotches are called "Sooty Blotch". Clusters of very small dots is called "Fly Spec". Both are caused by air-born fugal spores. They are both odorless and tasteless (at least to humans) and are evidence that the apple has successfully fought off the fugal attack, otherwise the fungi would have eaten through the skin. This also means that the apple skin has ant-fungal antibodies on it, which are good for human consumption (natural immune boosters).