Hey everyone!
I’m new here and on day 4 of keto 
I noticed last night that my blue veins have become more visible, especially on my thighs and arms. I’m a pretty thin girl so not sure if it’s from losing water weight or what but it freaked me out a bunch.
Does anyone have any insight?
Sorry, no insight. I guess you are going keto for health reasons other than weight? Someone on here will have some ideas for you. My only advice four days in is to not over-think it. Keep below 20 carbs, eat enough calories, drink enough water, you’ll be good. It’s too early to take much meaning from any changes. Avoid the scale for a while, if you can. And just do keto. It’s easy and you’ll feel great. If you lose the usual urges/cravings to eat, eat anyway. Just eat smart. It all works out. Trust.
Yes, health reasons I’m skinny but mind you…I’ve got a bit of cellulite I wouldn’t mind to lose. You can be skinny and unhealthy lol. But weight loss isn’t the reason I’m going keto.
Thanks for your response though, I’m hanging in there with the keto flu/withdrawal symptoms but it just shocked me seeing more blue around my body. Wasn’t expecting that!
Welcome and best wishes! I second everything @robintemplin says. You’re in 4 days. That’s diddly. Keto is a metabolic normalization process and normalizing weight is part of that. As long as you eat enough food, you will probably gain some weight towards what will be your ‘new normal’. ‘Skinny’ is not normal nor healthy any more than 'over’weight. Keeping up your fluids and electrolytes will ease any carb withdrawal symptoms you may experience. There is no such thing as ‘keto flu’. 
You may find this of interest:
Not quite the same thing (but maybe) but I experienced a lot of unexplained bruising when I began keto. It took a few months and suddenly they stopped showing up.
These are the result of not getting enough salt. If you increase your salt intake and drink to satisfy your thirst, you should be fine.