It's supposed to be 白薔薇 (Shirosōbi) Here are the pictures of white roses that came up when I searched for that word: https://www.google.com/search?q=%E7%99%BD%E8%96%94%E8%96%87&espv=210&es_sm=122&source=lnms&tbm=isch&sa=X&ei=z1GuUpXuLoGIrQfc8oGoCw&ved=0CAkQ_AUoAQ&biw=1366&bih=680 Hope my answer was helpful... ^_^

We say it 白バラ[しろばら] or 白いバラ[しろいばら] in general.

white rose 白いバラ

Let us hear the song once it's done!!! m(^ ^)m