Warm and cool: reading a palette from a photograph
Most layouts that look unplanned have the same problem: there are too many colours and no obvious order among them. A photograph can fix this, because it already contains a set of colours that belong together.
Take three, not eight
Open the picture and find the largest area of colour. That is your base, and in a photo of mandarins on white it is the white. Next, find the colour that draws the eye first: the orange. Then find the smallest accent that is still clearly visible, here the dark green of the leaves. Base, lead, accent. Anything beyond those three should be a tint or shade of one of them.
Check the temperature
Colours are warm or cool, and a layout reads as calm when one temperature dominates. Orange against white is warm, with a cool green as relief. If you add a blue button next to it, the blue will look louder than it should, because it is the only cool colour of any size on the page. Shift it towards the green instead.
Test it in grey
Turn the layout to greyscale. If the headline, the image and the button still separate from each other, the palette works. If the orange and the green turn into the same grey, the contrast comes from hue alone and a lot of readers, including the one in ten with some form of colour vision difference, will lose it.
Use the image, not a swatch
Sample colours with a picker from the picture itself, not from a colour wheel. Colours taken from a photo already carry the slight greyness of real light, which is hard to invent.