If you're a photographer today, you're sharing your photos everywhere from Facebook to Flickr. Your photos are being seen on every device possible, iPhones, Samsung Galaxys, crappy Dell office monitors, and Mac Retina Displays. Each online service, each device, even each web browser handles color differently. If you're putting your photos up online, you really need to think about how you output files for the web. If you accidentally save to the wrong color space, you can really change people's perception of your photos.
The first thing you need to understand is Color Space. Which basically stands for the range of colors utilized. Every Color Space has a Color Gamut which is basically the amount of colors in a color space. Every color space is different and will give you different results. You may have heard the term Adobe RGB 1998, sRGB, or ProPhoto RGB before. Those are generally the most used color spaces that you'll see when you're working with photos. Here's the difference in color gamut from those:
As you can see there's a pretty substantial difference between them, especially sRGB and ProPhoto RGB. This can become an issue for your photos when uploaded to the web. Chances are if you upload a photo exported to ProPhoto RGB, you're going to have an issue when people see your photos.
I was stupid when I set up Lightroom.... I thought "Well, it does have PRO in the name. It must be for professionals. So I'll use it". Well, I uploaded this to Flickr, Imgur, shared it on Reddit, Facebook, etc... I didn't even realize what happened until someone commented on how they loved the gritty editing to it. I had no clue what they were talking about, I looked at it on my phone and what I saw was what you see on the right. It looks awful compared to the original, and that was seen by over a thousand people. I don't know how many saw the correct version and how many saw the terrible version, but I know anyone looking at that on a mobile device saw the bad one. The problem with most mobile phones is screen quality. Not every phone has a retina screen and even if they do, they still won't have the same display quality that a decent monitor would have.
So now you're wondering what you can do to make sure you don't make the same mistakes as me. Convert to sRGB when uploading to web. Simple as that. In fact, I tend to make my edits in the sRGB color space because my customers usually just want digital downloads anyways. If you're not sure how to make sure your photos are being converted correctly, here's a couple tips.