Opinion and practice is divided with regard to tone marking in an alphabetic orthography for a tone language. Some orthographies don't mark tone at all, others mark tone phonemically, and others employ various other reduced marking schemes. This paper descibes tone orthography experiments in the Bafut and Kom languages of Cameroon, and goes on to examine the success of phonemic tone marking for the Dschang (Yemba) language of Cameroon, which has both lexical and grammatical tone. Participants with a variety of ages and educational backgrounds completed a reading and writing test developed to test understanding of tone marking. They read texts which were marked and unmarked for tone, then added tone marks to the unmarked texts. The results show that the existing tone orthography actually hinders fluent reading and writing. This finding highlights the fact that relatively little is known about the reading process for alphabetic orthographies decorated with tone diacritics. The author argues that any consideration of the linguistic and socio-political factors influencing orthography design must be complemented with experimental work that provides an objective evaluation of orthography options.