Saying that a button should use the same blue as another screen is hard to reproduce. PowerToys Color Picker can capture a displayed colour and copy its value in a chosen format. The number becomes more useful when it travels with the location and state that produced it.

Open the relevant page at a stable size and identify a flat area of the colour. Avoid a shadow, antialiased text edge or photographic texture when your intention is to sample a solid fill. Those areas contain multiple values even when they look like one colour at normal viewing size.

Select a value deliberately

Enable Color Picker in PowerToys and use its configured shortcut; the documented default is Windows+Shift+C. Check the selected clipboard format before copying. HEX is the default, while the editor can show other enabled formats such as RGB.

Zoom in with the mouse wheel to inspect the sampling area. Microsoft describes a useful way to capture an element's non-hover state: start close to it, zoom to freeze the image, then choose the point in that enlarged view. This avoids accidentally sampling a colour that appears only when the pointer is over the element.

Hand over a reproducible observation

Put the value in a note together with its format, the page or application, and a description such as normal button background. Include a small reference image if appropriate. Repeat the sample at a second point in the same flat region; different results can reveal a gradient or a mistaken target.

Treat the sample as an observation from the displayed content, not automatically as the organisation's approved brand specification. If an original design file or style guide exists, compare against that source before replacing a production colour.

Microsoft lists wide colour gamut and HDR formats as unsupported. Do not use this utility as evidence that a monitor is calibrated or that a printed colour will match. For ordinary interface handover, a checked value with its state and format is the practical deliverable.

Source: Microsoft PowerToys documentation.