I'm new to illustrator, just opened it up a new project. When I pick a new color from an existing image and save it in my color swatches it seems fine and vibrant. But when I color my objects (created with the polygon tool), the color turned out faded, more pastel-ish that expected. I never changed any settings and don't know what happend... It seems like the transparency has changed, but when the opacity is100%...
Has anyone else experienced this issue?
Please select one of those paths and show us the appearance panel.
Your layer has transparency.
Click the Layer item at the top of the Appearance panel and check the transparency.
I hope your issue is resolved by now. If not, in addition to suggestion given by Ton, please check out this help article(https://helpx.adobe.com/in/illustrator/using/transparency-blending-modes.html) to know how to edit artwork with transparency.
Hope it helps.