Yep chlorotic Gardenia.

HTH
CHris

Thanks - I have fed it an acid food last evening. Do you by any chance know what specific type of Gardenia it is ?

It's Gardenia jasminoides, also called hardy gardenia or Cape jasmine. There's many different cultivars and it's virtually impossible to tell them apart when not in bloom. Some of the most common cultivars are 'Chuck Hayes', 'Kleim's Hardy' and 'Veitchii'.

Chlorosis (yellowing) of the foliage is very common and is usually an indicator of iron deficiency or insufficiently acidic soils (which can create iron deficiency). Applying a fertilizer for acid lovers twice a year as growth begins in spring and again in late summer/early fall should help, but you can also increase soil acidity through applications of elemental sulfur or address the iron problem directly with supplements like chelated iron.