rdp1 Hi
1) For changing font color of menu items when the header section scrolls down, Try add this to custom.css file and change color code accordingly:
.s5_wrap_fmfullwidth li a{color:#fff !important;}
Finding custom.css and you may create a new file with similar name (if it doesnt exist) ::
Shape 5 templates ship with an empty custom.css file in the /css/ subdirectory of your template. Simply add your styles to this file and they will be included in your layout.
Kindly ensure to clear your browser cache if changes dont reflect
2) For logo if you wish to refer to part as seen in screenshot, The image doesnt get changed when header section scrolls down however, The text part gets inverted with CSS filter Property