#1. The screen is too bright.
#2. You are too close to the monitor.
#3. You may be susceptible to the temporal dithering process.
#3 - Inexpensive LCD monitor like the Samsung 2493HM uses a TN panel which is not capable of truly producing 16.7m colors. Instead it can only truly produce about 256k; which is why they are inexpensive to manufacture. Thru a process call temporal dithering, the TN panel flashes very rapidly between two colors to produce a color it normally would not be able to produce.
Example, suppose a TN panel cannot produce purple, what happens it the pixels in the TN panel will quickly flash between red and blue. It's so fast that your brain thinks it is looking at solid purple.
The only way to determine if #3 is the issue is to try using another TN panel for a prolonged period of time to determine if you have the same issue. The monitor should be fairly recent because temporal dithering is a recent tech that is replacing spatial dithering.
Spatial dithering basically will create a checker board pattern of red and blue to create purple (using the example above). This can cause visual artifacts and color banding issues which is why this method is being dropped by manufacturers.
If #3 is truly the issue, then you need to buy a monitor that uses a PVA, MVA or IPS panel. Those monitors will be more expensive because those LCD panels can truly create 16.7m colors without having to use dithering to trick your brain. A 24" LCD monitor using one of these panel techs will start at about $600 online when there is no sale or coupon.