If they're not in a feminine color/pattern and are paired with reasonably masculine, edgy clothing above the waist, they can look okay on a slim young man in a fashion-forward environment. Otherwise, they probably will look silly.
Wear linen, because it probably will be hot. Although many tourists wear them, avoid shorts if trying to look stylish. Shorts generally are frowned upon in Europe. Bring an odd jacket (maybe a 1-button) for not-so-hot evenings, because that's what many men wear to nicer establishments.
For someone with an overly large upper torso, boot-cut jeans might actually be better than straight leg. (Definitely avoid skinny jeans.) Anyway, it wouldn't be hard to come up with something decent, provided the fit is made right. The harder part is figuring out what specifically that style is, for age, location, occupation, etc. have not been stated. This isn't the section for haircut advice, and the pictures so far don't show enough of the face to enable informed advice...
Bad news first: it's time to be concerned about a receding hairline.
That said, for now it's still an attractive head of hair and shouldn't be cut short. And yes, the forehead shouldn't be highlighted. Here's an idea for older but still youthful...
In that situation, if a man is average height with average proportions, there's almost no restriction on pants color if the tie (maybe not included) or perhaps shirt is attention-getting. If for example the legs are long (in absolute or relative terms), then mid-gray, medium brown, and dull olive would be the best options. With tan shoes, it's especially important to make sure the clothes put most of the attention near the face.
Light brown tends to be problematic for belts or shoes, because it can draw attention to a large waist or large feet, respectively. That is, if the suit is in the darker half of the color spectrum. Most people seem to automatically avoid mixing light brown with that. [enter speculation about the suit colors most often paired with brown ties]
That would help explain why dot ties, dot shirts, etc., have never been very popular. There probably are non-style implications that others can think of.