When you are designing your website or simply uploading images for your content there are times you might have problems with images keeping the same appearance you saved them as on your computer.
Now before we get into the problems with uploading files lets first take a second to understand how photoshop can cause this problem.
Often when you are working on images you want to optimize them for size and Photoshop has this feature that can help you save three main file types for the internet. If you are working in Photoshop and decide to save a JPG file you should understand that the image will change depending on your settings. It may only appear slightly different or it may be dramatic depending on the level of compression you use. Gif files are another problem because they have a lower limit of colors that can be used to represent the image through dithering. Finally PNG files normally preserve the original image if you pick 24bit color because it is not lossy like JPG or restricted like GIF.
Ok so always preview your images locally before you blame the internets. You can do this by simply dragging the image into your browser or by assembling your html page and viewing it locally before you upload it.
So back to problems that actually can be a result of uploading images.
If you are using WordPress or a Gallery Application on the internet to display images most of these programs will resize and optimize your uploaded images automatically. If there is any processing of the image by GD or imagemagick the two most popular php image processors you can expect either slight or dramatic changes to your images and this is before you apply any special filters like the ones you like on instagram.
The problem is similar to what photoshop can do to your images when you save for web.
If you know that it is important to preserve the colors in your images for items such as Logos or Backgrounds then you should double check these images before uploading and then use a FTP program to upload them in Binary format.
Most webhosts provide FTP Uploads the exceptions are sites like WordPress.com that host you through their application.
Always double check your images in a browser .. in a html file showing your page layout and css colors if necessary.
Upload special images that must remain the same by FTP not into your Gallery.
and Use PNG when colors must remain the same.