In the global.json file in the lighting folder, the following line suggests that all blocks have a default mer of zero reflectivity, zero illumination, and total roughness:
"pbr": {
"blocks": {
"global_metalness_emissive_roughness": [0.0, 0.0, 1.0]
However, the actual default mer of all blocks with sky reflections turned on seems to be [1.0, 0.0, 0.0]. Basically, when using a shader with no heightmaps and only default textures, everything looks like it's covered with foggy glass. Also, sky reflections seem to pass through any block light passes through, such as stairs and slabs.