Thank you promethuem5, the things you pointed out did nag me, but frankly, I did use decal softer for them, but didn't work very well, especially on the dark color area, I guess a gloss coat under the decals is the ideal way.
And let's continue...
After the assemble, I used Gunze's Mr. White Surface 1000 for coating, it coule help you to check if there is anything not that good on the surface and can be as the color paniting basis, especially for the rubber parts.
I used Alclad 2 Jet Exhaust mixed with some drops of Pale Burnt Metal for the metal color.
Then I made the pre-shading, I used Gunze's Navy blue and NATO Brown.
I used Gunze's c318 Light Grey mixed with some white for the basic color.
Then I used even whiter grey for the high-light areas, and NATO Black for the strips, for me, pure black is too black. In the actual world nothing is pure black due to a lot of reasons esecially the sun light and air.