I agree, your issue is most likely one of misinterpreted RGB values.
Those RGB values don't have absolute meanings, what they look like is highly device specific. In order to have them displayed correctly on the output device you would have to know how the output device behaves (i.e know its profile) and calculate the RGB values with that in mind.
This is obviously not feasible for images that are to be viewed on thousands of different people's monitors. Hence, you encode your RGB values for a hypothetical device, such as the ones characterised by sRGB or aRGB. It is then up to the viewer's end to make final adjustments in order to account for differences between sRGB/aRGB and the real output device.
Those final adjustments depend on a) the viewer knowing how to correctly interpret the sRGB or aRGB values (i.e. knowing what they mean in absolute colour terms, such as CIE LAB or CIE XYZ), and b) to know how the display monitor behaves (i.e. knowing the display device profile). It can then transform the RGB values in your image file to CIE LAB or XYZ, as prescribed by the sRGB or aRGB profile, and from there build RGB values to send to the video card/monitor according to the display device's profile.
Both a) and b) are often not given for viewing with web browsers. First, the browser is usually agnostic to profiles (most quietly assume something close to sRGB) and second, they don't make use of the platform's colour management features (if any) to take advantage of the monitor profile (if any).
Hence, the common situation is a web browser that interprets RGB values in image files according to sRBG (or thereabouts), and a monitor whose profile is either not known or not used by the browser. The best you can hope for in that case is that the monitor has been calibrated to something close to sRGB behaviour.
As file creator, the best you can do is convert your files to sRGB upon saving. That way the majority of colour agnostic browsers and un-profiled monitors might still get a reasonable approximation of what you had intended.
Alternatively, you can hope that most members of this forum view posted images with colour management aware software and use accurate profiles for their monitors...
Cheers
Steffen.