I'm a graphic design student and one of my designs is a pink 桃色 rose 薔薇 = (桃色薔薇). I read that Japanese is read right to left and also horizontally? I want the design's first line to pink and under that rose. I just want to make sure it's correct. It is simply 桃色 and under it 薔薇? Or something else?
Your source was wrong IF you are talking about horizontally written Japanese.
There are two ways to write Japanese sentences (in terms of character positioning). If you are going to write your characters horizontally, you will write it like you do in English. Start in the top left, go right. When you finish that line, drop down a row and continue.
The second way is what can be confusing to some (including your source). In this second method, you start at the top right corner, and write each successive character below the first until you finish the column, and then go left one column, and repeat the process.
Both methods are so common that the spacing is done such that it should be visibly obvious which format is being used.
Of the two formats you included, the left format is written in the correct order. It should be noted, however, that because 桃色 is a の-type adjective, you should have の in between your words for pink and flower like this:
Otherwise it is grammatically incorrect.
Japanese written horizontally is read left to right, top to bottom.
Japanese written vertically is read top to bottom, right to left.
This resource might be helpful.