What you first see is the camera’s embedded JPEG preview, not the fully rendered RAW file. That preview includes the camera’s own processing, such as picture style, contrast, saturation, sharpening, and white balance interpretation. When Aperture renders the RAW, it applies its own RAW conversion, so the result can look flatter or different in color.

In general, Aperture should use the camera’s white balance setting as a starting point, so a strong yellow shift is not typical. If that happens consistently, check whether an import preset or white balance adjustment is being applied automatically.

If your goal is to keep the camera-rendered look, a practical option is to shoot RAW+JPEG. Then you can use the JPEG when the in-camera rendering already looks right, or use it as a reference while adjusting the RAW.

If the issue is more about the RAW looking less vivid than the preview, that’s expected: the camera preview usually has extra processing applied. Using an import preset such as Auto Enhance can make Aperture’s initial rendering look closer to what you saw on the camera.