If you do not observe fossils skip it in your description, avoid using the negative i.e. nonfossiliferous. If you see no stratification, skip it . Unless the user has further specified these terms assume that they are synonyms. I prefer to use the name mudstone but most field geologists seem to use shale instead. Siltstone generally get used if and when one can see grains in the rock with the handlense.
Color is a very important part of the description of mudrock.
The problem is that what is brown to me may not be brown to you. Most field geologist ignore this problem and call it as they see it and assume that the next guy will have no problem. Color chart for the field description of sedimentary rocks. D.C. Goddard, E. N., Trask, P. D., DeFord, R. K., Rove, O. N., Singewald, J.T., and Overbeck, R.M., 1970. Geological Society of America, Boulder, Colorado.