[Kartiky14]

Is there anyway to guess the colour of a metallic oxide by just knowing the colour of the metallic ion???
For example
ZnO??
Zn+ is a colourless ion??
 

[Arkcon]

I've never heard of a direct correlation between oxide color and ion color.  Generally, many transition metals that have colored solutions, and salts and generally, the Alkali Metals and Alkaline Earth Metals are always white, but I can't rule out an exception.

[vmelkon]

Is there anyway to guess the colour of a metallic oxide by just knowing the colour of the metallic ion???
For example
ZnO??
Zn+ is a colourless ion??
 

That's Zn²⁺

ZnO is white. Are you suggesting that if the metal ion is colorless, that the oxide is white?
Because Ag+ is colorless but silver oxide is brown.

Another example is Cu²⁺ is blue in water while CuO is black.

[fuyuki_kaze]

well, according to my observation, s-block metal usually have white salt when powdered(colourless solution), but i think they are more like transparent in a big chunk, just like rock salt, but im not sure
i think it is because there are no extra electrons to disturb the light.
also for the reason why the CuO colour is different from Cu2+ solution,. well i didnt study much on d-block element yet, but as i heard of the colour of d-block element is given by the extra electron in the d-shell, but why CuO is black... i think its about the structure, well, wait for the pros to answer=w=

[AWK]

Cs₂O - yellow-brown

[Arkcon]

well, according to my observation, s-block metal usually have white salt when powdered(colourless solution), but i think they are more like transparent in a big chunk, just like rock salt, but im not sure

And then,

Cs₂O - yellow-brown

And that is what I meant when I said ...

I've never heard of a direct correlation between oxide color and ion color.  Generally, many transition metals that have colored solutions, and salts and generally, the Alkali Metals and Alkaline Earth Metals are always white, but I can't rule out an exception.

You can always find an exception.  There is simply no hard and fast rule comparing ion in solution color to color of another compound that contains that element.