"Better picture quality."
You use this sentence.
If we say picture quality When comparing two lenses, we rarely speak of something in which one "… is less dark and provides more vivid colors". ¹
These things are more a function of light in the scene. The photographer's ability to see and capture this light while at the same time assembling the frame is so that our attention is directed to what the photographer wants to focus on and how information captured by the camera sensor is converted into an image. Increasing or decreasing the contrast, white balance, saturation, exposure, etc. have the most impact on the things you deal with.
The types of images you see on 500px, Flickr, or even Instagram that many people call "vivid" are usually not straight from camera JPEGs created with the camera's built-in development settings. These are raw images that have been processed with configurable applications such as Lightroom to make them look the way they do. They weren't usually caught in the hard midday light either.
If you switch from your 18-55 kit lens to an 18-100 zoom with a wider range, your photos will no less become darker or more vivid. Generally, an 18-55mm lens usually results better Image quality than with a similarly manufactured 18-100mm lens. The larger the range between the extreme values of the focal length of a lens, the more difficult (and expensive) it is to produce a lens with high optical quality. But even if the 18-100mm lens has "better picture quality", it won't make any difference to the things you address in your question.
In terms of lenses, picture quality it's about things like accuracy ("sharpness"), geometric distortion, peripheral light decay, etc.
The whole point of one Interchangeable lens system The camera is said to allow you to use different lenses that are better or even great at one point, but unsuitable for other things. Fixed lens cameras force you to use a single lens that is mediocre or worse in many situations, but nothing better. It's not much different than using a fixed lens camera with a single lens camera when using a replaceable lens. In some cases, the fixed lens camera may meet your needs better than a single lens ILC.
The best lenses are all prime Lenses. That means a single focal length. No.Zoom.At.All. They are really good at providing the field of view and other features you need. This is because they can be optimized for a focal length. A good 100mm macro lens with a flat field of view differs from a good 85mm, 105mm or 135mm portrait lens. However, they are not very flexible, so you will need a lot for different things. Some are pretty good for not much money (e.g. EF 50mm f / 1.8 STM @ 120 USD). Others are incredibly good for a shipload of cash (e.g. EF 400mm f / 2.8 L IS II at $ 10,000). Most fall somewhere in between.
Compared to zoom lenses, prime lenses, in addition to the same or better optical quality at a lower price, can also be smaller / lighter, have a larger maximum aperture and can often be much cheaper.
Short ratio zoom lenses, i.e. H. Zoom lenses with a difference less than three times between the longest and the shortest focal length can also be very good. But the best cost a lot.
If you move outside the 3-fold limit, the image quality becomes noticeably worse. Some 4-5x zoom lenses that fall completely within the telephoto range can be pretty good. But if you try to design a lens that goes from wide-angle to telephoto and covers a zoom range of 5X-10X or more, it becomes really difficult to keep it affordable and manageable in size and weight, yet still provide excellent Picture quality. You typically get better image quality and spend less on something like an 18-55mm and 55-250mm pair of zoom lenses than on an 18-200mm all-in-one.
¹ Sure, we can measure the T-aperture (light transmission towards the aperture) of one lens against the other. We can measure how each lens affects contrast and color. In the "dark times" of the manual focus film era, these considerations were more important. We couldn't change the ISO or color sensitivity curves every time we took a single roll of film. In the darkroom, much more work (i.e. time and money) was needed to fine-tune color, contrast, etc. than we can now do with raw digital data. These very small differences in transmission and color can now be corrected easily after the picture has been taken. On the other hand, digital sensors are much flatter than films and can resolve more details than films with 35 mm sizes. We now expect a lot more from our lenses in terms of resolution than we did then. Most 35mm photos were never printed larger than 8×10 in the film age. Now we routinely look at everything we shoot under 100% pixel peeping viewing conditions, which is equivalent to enlarging to 60 x 40 (24 MP on a 23-inch HD monitor).