My photos are coming out grey?

I'm new to photography and I'm trying to take photos of sneakers. I have an all in one light tent (http://www.amazon.com/gp/product/B012CFI7TG?keywords=Torchstar&m=ACSOVW5LP5G75&qid=1458057711&ref_=sr_rp_1&sr=sr-1). Also, I'm shooting with my iPhone 6s Plus. Is there an app I can use to take better pictures or do I need to use a DSLR camera? What am I doing wrong?

All camera light meters (including those in a mobile phone) meter for a mid tone 18% grey. You need to dial in about 1.5 to 2 stops of exposure compensation (ie set EV comp to +2).

Your phone is not ideal for this - it's likely also bumping up the ISO. You need to keep this down, which will require the phone to be stabilized on a tripod.

Something like Camera+ will give full control over the exposure. With sufficient and correct lighting the Iphone should be more than capable of getting a decent photo.

Is it the background that's grey or the sneakers?

It would have been more help to show the photos you've taken rather than the photo of the light tent.

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