That`s only the paste, not the stain. Try using recipe from Henna Guru and buying fresh good quality henna (the stain on the chest won`t be chocolate brown cos skin has diferent thickness but it can have nice light brown shade ).
The one from Henna Guru is quite cool (but if your henna is stale or your room is cold or model`s skin is cold results can vary, just keep henna and your model in nice warm place (you can wrap henna paste after it dries in tissue or toilet paper, it will help to keep te warmth and make the stain more visible). Remember to use good quality eteric oils, they will hepl you to achieve darker stain.
Oils (cajeput, tea tree) darken the stain (the darkening process is also faster) but shorten it`s longevity. And lemon juice... Some sources say you don`t need it at all (like in the recipe from Henna Guru), I`ve tried the recipe... And henna was perfect so I don`t use lemon juice in my paste anymore (I only use sugar+ lemon juice sealant).