Typically, touch-up coats will be lighter in color if they are applied when the temperature is 10 degrees cooler than the initial application. If the reverse is true, the touch-up coat will appear darker. Color differences with warmer temperatures—over 60 degrees—are less predictable.
The real problem is likely: Paint is a little bit like wallpaper runs. The touch up paint you picked up is from a different batch than the original paint and the colorants used to tint it are also (most likely), so the paint is slightly different in color.
When painting a wall, the color often appears lighter as it dries. This is because the paint loses some of its moisture and gloss, revealing the true color underneath. However the final appearance can also depend on the type of paint used (eg matte, satin or glossy) and the lighting conditions in the room.
Paint touch-ups usually look darker because there is less moisture (and therefore more pigment) in the touch-up paint than the original paint coat. Less moisture in the paint will mean that the evaporation and wicking will happen at a different rate than the original coat of paint which will cause color differences.
Wall patch tends to soak up a LOT of paint, much more so than the existing paint on the wall. Because of this, a small area of patching can stand out like a sore thumb. You can minimize this by priming in the patched area with a primer so it comes closer to matching the rest of the wall.
Use a roller, if possible — A roller will give you better quality and blending than a brush. The preferred roller is a "weenie" roller with a good, quality synthetic cover. Choose a nap thickness of ¼ - to ½ inch. Use less paint — When loading the roller, use the least amount of paint necessary.
Alkyd paints are shinier and may take from a week to a month after touch-up to blend with the original paint coat. Latex paints touch up easier, regardless of the gloss level, but can still take several days to blend with the original color.
The number one reason paint looks different on the wall is lighting. Natural daylight brings out the truest color, while incandescent lighting can warm up tones, and fluorescent lighting can cast a cool glow. Always consider the primary light source in your room when choosing a paint color.
Temperature, paint film thickness, flash off time between coats, fluid tip sizes, speed of the spray gun, surface type (Plastic or Metal) and humidity will all cause the color to shift lighter or darker. The rule of thumb: the longer it takes to dry, the darker the color will change as it dries.
Use Mineral Spirits. Mineral spirits are solvents that remove paint from many surfaces including your car. Many at-home DIYers use mineral spirits to remove dried paint from a touch up job that didn't go as planned. Mineral spirits effectively thin and remove paint and work well on your car when used carefully.
"Touch-ups" are most commonly done after painting is done to achieve a nice blemish-free surface. Whether it's to conceal minor repairs or cover defects and marks, ideally, touch-ups should blend with the existing paint colour.
If Paint is Too Light
Use other paints of the same brand, type, and sheen to darken the paint.
If you mix the paint properly, it should look the same as the color you picked out once it dries. It can take paint up to eight hours to fully dry, so wait at least that long to be sure the paint has taken on its final appearance.
“Yes, applying a second coat of paint will usually make the colour appear darker and more saturated. This is because the second coat adds more pigment to the surface, reducing the amount of light that passes through the paint film.
Use a Roller
Rollers are great for getting large sections of paint on walls without having to worry about brush marks!
Typically, touch-up coats will be lighter in color if they are applied when the temperature is 10 degrees cooler than the initial application. If the reverse is true, the touch-up coat will appear darker. Color differences with warmer temperatures—over 60 degrees—are less predictable.
When paint is wet, it tends to appear darker due to less light reflection. But as it dries, the water evaporates, causing the paint's hues to lighten up. Oil, acrylic, and latex paints are exceptions to this, appearing darker as they dry.
When done correcly, a touch up that is wet sanded will disapear and looks as if nothing has ever happened to the paint. The difficulty with that is you need to let the paint cure before wet sanding. With modern paints, that is at least 24 hours.
Manufacturers will typically say that a paint will dry on average in about an hour but in reality it's going to take 30 days to cure and reach its full optimum hardness.
Paint ghosting happens when dust, soot, or other airborne particles cling to walls and ceilings, forming subtle, shadowy patterns. These patterns often show up on cooler surfaces where moisture tends to settle, creating ideal conditions for particles to stick.
It is virtually impossible to reproduce the exact wicking rate, and this is why a touch-up job will often appear as a slightly different color than the original paint. Another factor at play is fading, which happens regularly to the paint on your walls over time.
Dilute the paint by 5 to 10 percent with water for latex-based paint or mineral spirits for oil-based paint. Stored paints can lose moisture, making it more difficult for touch-ups to match the original coat.
Simply use a machine buffer and your favorite polish once the paint has dried completely.
Using a paintbrush, start at the center of the touch-up and slowly move outward. Lightly extend the tip of the brush just beyond the area you're touching up to seamlessly blend the touched up area with the original painted area.