Changing background colour on things to ease reading is a cheap and simple way of making some things more accessible. You can't always rely on colour changing options to be available or very well implemented.
Hardware reading rulers are very effective and I definitely recommend trying them as a cheap solution for anyone struggling to read. I recently purchased some Crossbow Reading Rulers and coloured overlays for a family member from The Dyslexia Shop for little over £10 for two overlays and two rulers.
Now attaching overlays to your monitor is ugly and requires your monitor to be a set size as well as being silly if there is software out there. I have been looking at software which will provide a whole-screen tint of a colour of the user's choice.
This is a quick and dirty review of some apps I have tried to use for this purpose
Screen Tinter Light - FREE
This is a free app I found out about via a DSA assessment. If it worked it would be nice, but it does this weird half-attempt at background colours, so half of the application's window frames (there's a word for that isn't there!) but not the contents of the window. It doesn't evenly tint all the screen, just somebits of it so it looks like the graphics card has dropped back to 16 colour mode, or you've got a splitting headache. I wasn't impressed.
Crossbow Virtual Reading Ruler - £20ish
This is a piece of software written in Java for Mac or PC. It allows a mobile overlay to be put over any part of the screen. The settings once you can get them up as the java-ness makes it a bit unresponsive are lovely, very clear and easy to use. They have some nice default settings and lots of tweakability for advanced users.
Shame that you can't make the overlay bits lock, what they seem to mean by lock is that the overlay follows mouse. What I wanted was something I could say "lock over screen" while still allowing me to click on things underneath the overlay as it were. With this one, if you click on something which is covered by the overlay bit the overlay gets selected. that becomes obstructive when you are trying to get on with using your computer as normal.
You can't get a free trial of this. A downloadable version for 1-3 machines is £17.99
Claro Screenruler Bundle - £100ish outside of DSA
This is a part of Claro's software collection which is often bundled in with Claro Read. The copy I used for review was the standalone Screen Ruler bundle which is a CD and USB stick both containing the software. I have currently only had time to play with the usb stick. On plugging it in, Windows picks it up, does the usual recognising hardware thing and gives you an option to choose which bit you would like to use. I'm wanting a whole screen overlay so I chose that. Sometimes it pops up the "what app do you want" dialogue twice which the user has to close instance #2 of.
On first opening the settings menu pops up giving the user a choice of colours and opacity of those colours. These aren't as flexible as the Virtual Reading ruler but they're fairly self explanatory. Once you are happy with the colour you click OK and the application minimises to the system tray (bottom right hand of start bar). You can carry on using windows as usual. You then have your usual computer but with tinted overlay on top of it. It doesn't interact with anything unless you open up the settings by selecting it from the system tray.
Glitches noticed in testing were that sometimes it doesn't tint my start bar and sometimes it does. I'm running twin monitors and it will only tint one screen at a time with tint changing monitor with mouse location On a colleague's machine it didn't tint the content part of the windows in Microsoft Applications. More testing needed I think.
You can download 15 day free trials for mac and PC from Claro's website
Zoomtext - £400ish for nonreader version
Zoomtext is going to be overkill for most users but is worth a quick mention as I have come across people, usually who have visual impairments who need very specific colours changing, or need to do complex things with contrast, brightness or tone down one particular colour or enhance one other particular colour.
Where none of the other packages did what was needed Zoomtext was believed to be suitable as well as providing a bit of zoom function. You can download a 60 day free trial from AI Squared the software company and have a play.