"An orange petticoat"
pais oren because the adjective usually comes after the noun in Welsh. There is no indefinite article (= 'a/an') in Welsh, so nothing specific to translate there. mae is a verb, 'is' or sometimes 'there is', and unnecessary in this case.
- pais oren - (an) orange petticoat
- mae pais oren yn y peiriant golchi - there is an orange petticoat in the washing machine
Remember the vast majority of adjectives in Welsh follow the noun which is why the answer is 'Pais oren'